α-amylase as an important industrial enzyme was widely used in food industries, textile technology, paper manufacturing and so on. In this study, the method preparing dextrin with different DE value by combination of common and thermalα-amylase was investigated. Dextrin with different DE value was used as carbon source and its effect on enzyme production was studied. Medium and conditions of fermentation were optimized using quadratic regression revolution design. The properties ofα-amylase produced by B.subtilis ZJF-1A5 were studied. The batch process and dynamics model were studied and medium-scale up was also investigated. The inducing mechanism of dextrin with different DE value on production ofα-amylase by B.subtilis ZJF-1A5 was discussed. The main results were as following:1. By successive use of double-enzyme method (medium-temperature and high-temperatureα-amylases), the method preparing dextrin was obtained, which could reduce the time of enzymatic hydrolysis and addition of enzyme. According to the result of single-factor experiment, an orthogonal test was designed and carried out, the optimum condition was determined as follows: reaction temperature 90℃, hydrolysis time 20 min, addition of medium-temperatureα-amylase 4 U/g starch and addition of high-temperatureα-amylase 7 U /g starch. On the basis of above conditions, dextrin with different DE value could be obtained by adjusting the hydrolysis time or enzyme addition.2. Starch was treated by ultrasonic and then hydrolyzed by the method of medium-temperature and thermalα-amylases, the molecular distribution of the obtained dextrin was more even. The ultrasonic conditions were as following: ultrasonic power 50W, total stimulation time 5-15min, ultrasonic stimulation time 2-5s and ultrasonic intermissive time 20s. On the basis of above conditions, dextrin with different DE value could be obtained by adjusting the hydrolysis time or enzyme addition. It was considered by integrated analysis that the surfaces of starch granules were subjected to erode and the pasting viscosity of starch decreased. The molecular weight distributions of dextrin by enzyme method with ultrasonic assistance were more even. The proportion of large molecules in the product reduced while the amount of linear molecules increased.3. The particle of the dextrin changed significantly compared with the starch. The obtained dextrin subjected to enzyme hydrolysis showed the narrowest size distribution. The crystal type of A -type of dextrin with DE value below 22 had been partly preserved and possessed crystal structure and the peak intensity was gradually weakened with the increase of DE value. This result revealed that amorphous areas composed of amylopetin (in coral regions of starch particles) were hydrolyzed firstly in the process of the enzyme hydrolysis. Apparent viscosity of dextrin with different value decreased with the increase of DE value. TG analysis showed that the thermal stability of the dextrin was higher than that of the raw starch. Transmittances of dextrin with large DE value were higher than that with low DE value. Gel filtration chromatography by Sephadex G50 showed the amount of linear molecules of dextrin with larger DE value increased. HPLC analysis showed molecular weight distributions of dextrin by medium-temperature and high-temperatureα-amylases method were more even and contained large proportion of glucose, maltose, maltotriose and maltopentaose in the components of oligosaccharide the polymerization degree (DP) was below seven.4. Yield and activity ofα-amylase were relatively high when the DE value of dextrin was controlled in the range of 16-22 and inoculation amount of B.subtilis ZJF-1A5 was 3%-4%. Single factor conditions of fermentation process parameters were temperature 37℃, pH 5.0, rotation speed 210 r/min and the culture time 54h.Regression equation was obtained by quadratic orthogonal rotation and the equation was as following: Y = 151.6 + 14.7 X_1 - 7.8 X_2+ 26.9 X_3- 19.7 X_1~2- 4.5 X_2~2+ 6.8 X_1X_3. The optimum parameters were determined as follows: temperature 37℃, pH 5.0 and the culture time 58 h. Theoretical maximum ofα-amylase activity reached 206.5 U/mL. And the product has a good application prospect.Compared with starch and glucose, dextrins with DE value 16-22 were used as carbon source in shaking-bottle incubating test, the activities ofα-amylase increased by 80.2% and 219.3%, respectively.The pilot test in 5L automatic fermentor showed that theα-amylase activity reached 469.8±27.7 U/mL when dextrins with DE value 16-22 were used as carbon sources. Compared with starch used as carbon sources, theα-amylase activity increased by 41.9%.5. The properties of a-amylase by B.subtilis ZJF-1A5 were studied. Its optimum temperature was 60℃. Its optimum pH of was 6.0 andα-amylase activity changed little at pH 4.0. So the enzyme was a kind of acidα-amylase and has perspective application in industry.The result showed that Mg~(2+), Ca~(2+), Na~+ and Al~(3+) were the activators ofα-amylase produced by B.subtilis ZJF-1A5 and activation ability of Al~(3+) was the strongest. At present there was no report about that Al~(3+) activated the activity ofα-amylase.6. The yield ofα-amylase by B.subtilis ZJF-1A5 increased by using dextrin with a certain DE value range as carbon source. The effective induced component in dextrins might be oligosaccharide. By ordinary fermention with oligosaccharide as carbon source, the results showed that inducing activity of maltopentaose was the strongest. It further confirmed that dextrins played important roles during the process of production ofα-amylase by B.subtilis ZJF-1A5.