Abstract: A preliminary study was made for the model of the tillering growth and decline of the rice colonies; which was analytically estimated with the agro-climatic data of 1973–1979 in Shanghai suburbs. The estimating result approximates to the observed value. The model we describe is yx=ao+(af–ao)e[–e(d–x)2]/x2 Here, yx represents the total number of rice stems in unit area when the accumulated temperature is x, which is accumulated by the effective temperature above 10 ℃ since the transplanting of the rice seedlings, ao is the basic seedling number in unit area, at is the total stem number in tillering peak, and c and d are experiential coefficient which are calculated with experimental data. For the stem number of a single plant, the model is expressed by yox=1+(aof–1)e[–e(d–x)2]/x2 The actual data were used to illustrate that the model mentioned above is applicable not only to both Japonica and Indica rice of all varieties, but also to the description of the regional mean tillering state. When afo is unknown, it can be calculated with its associated light and temperasure conditions.