Fire-preventing forest belts are widely used in south China. And the technique becomes a main countermeasure of forest fire prevention. But there are some problems need to be settled, such as the way of fire-preventing tree species selection, suitable density, structure and location of the belts. We do the research in order to perfect the technique. The fire-resistance order of 48 tree species is arranged through analyzing its ingredients. The decomposing characteristics of the leaves and twigs are analyzed through the experiments of thermo-gravimetric analysis. Using cone calorimeter, we studied the combustion of nine tree species. The theory analysis is done about the fire-preventing forest belts. Test of simulating the belts preventing fire is done in order to expose the mechanism of fire preventing. The results is stated as follow: 1. The best fire-resistance tree species are Schima superba, Camellia oleifera, Exbucklandia populnea, Michelia macclurei, Viburnum awabuki, Alnus nepalensis. 2. The speed of leaves losing water relate with its structure. Large proportion of xylem benefit to the water transfer. The high duct proportion is benefit to transfer the water in twigs. 2 According to the results of the thermo-gravity experiments, we establish the dynamic model. The two steps of gravity loss can be described by the two grade model。Compared the active energy of the sample combustion, we can draw the conclusion that thermo-stabilization of Schima superba, Camellia oleifera and Exbucklandia populnea is better than Pinus massoniana and Cunninghamia lanciolata. 3 The combustion process of nine tree species is measured by using cone calorimeter. Fire performance index shows fire resistance ability of the samples. The value of FPI of Schima superba, Camellia oleifera and Exbucklandia populnea are high. That means its have strong fire resistance. 4 The defoliation of Schima superba burn slower than that of Pinus massoniana. And it can't burn fully. Its burning release more carbon monoxide and smoke than pine.