Based on a comprehensive analysis of the previous studies about the effects of nitrogenpus fertilizers on rice tiller which is the most important component of rice population , the thesis was undertaking to study regulation mechanism of nitrogen nutrition on tiller development using plot, pot and solution culture experiments in two seasons of 1993 to 1994. The major work was focused on the following three aspects: nitrogen content of different organs at rice tillering stage(RTS relation between tiller production and nitrogen-supply level or leaf nitrogen content; effect of nitrogen dressing at different rice growth stages on the percentage of effective tiller (PET) that is an essential indicator of rice population quality(RPQ) and on population quality index. The results are as follows:1. The nitrogen content of leaf blade and sheath for the whole rice plant declined during tillering stage, with a sharp decrease at early tiller and slow decrease at later period. The nitrogen content(LBNC) of single leaf blade is highest at leaf emergence and lowest at leaf death. The LBNC of single leaf in RTS could differ 1.5 folds among nitrogen application treatments. LBNC for high nitrogen-supply level was higher and kept higher for longer time(l to 2 phyllochron) as compared to low nitrogen-supply level. The LBNC of 3rd and 4th node and leaf sheath nitrogen content(LSNC) of 4th node from top were most sensitive to nitrogen-supply level, and thus could be used as an indicator for nitrogen-supply level.2. The nitrogen-supply levels affected the emergence and development of tiller, and also changed the synchronization rule of n-3 between leaf and tiller emergence resulting over or down-synchronization rule, i.e., n-2 or n-4. There was a significantcorrelation between the nitrogen-supply level and tiller rate or relative tiller rate(RTR) from 0 to 70 PPM. The emergence of tiller in n node was regulated by LBNC and LSNC of n and n+1 nodes, also significantly correlated with LSNC of n, n+1 and n+2 nodes and LBNC or LSNC of n-1 node a week ago significantly. LBNC of n+1 node was decided by' LSNC of n node a week ago. As a result, there was an association chain from higher LSNC of n node to higher LBNC of n+1 node to emergence of tiller in n node. The optimal nitrogen-supply level for tiller emergence was 50 to 70 PPM. For the cultivar with 17 leaves in main stem and 5 elongation internodes, when the LBNC of 1 Oth node was higher than 3.35±0.14%, the tillers became effective. Whereas, when the LBNS of 13th node was lower than 2.35±0.06%, the emergence of tiller ceased.3. Over application of basal and tiller nitrogen fertilizer(BTNF) resulted in more abortive tillers, number of tillers decreased quickly after the peak of tillers number and lower PET. Yet, optimum application of BTNF resulted in steady increase and decrease in number of tillers and higher PET that was necessary for high yield of rice. Although more application of BTNF could accelerate the leaf emergency at early stage, the RPQ and yield of rice could be decreased even more. Thus, BTNF should be applied in an appropriate amount. Increased application of nitrogen fertilizer for panicle and grain (NFPG) by decreasing BTNF application could raise the chlorophyll content in last five leaves and delay their functional period, which could enhance photosynthetic production during the grain-filling stage. Increased application of NFPG by decreasing BTNF application also improved a number of indicators of RPQ such as specific leaf weight, ratio of grain to leaf area and weight of stem leaf sheath per stem. If total nitrogen application was 15kg per ma and the ratio of BTNF to NFPG was 5 to 5, the highest yield of rice could be obtained for the cultivar with 17 leaves and 5 elongation internodes in main stem.