The vertical distribution of primary production of phytoplank ton in various seasons and its relations with li,ht intensity, temperature, chlorophyl a.transparency at the mouth of Meiliang Bay in Taihu Lake from Aug.1991 to Feb.1993 were studied.The results show that temperature is the main factor to affect the primary productivity, and the annual primary productivity was mainly distributed in summer, June to August.The maximum value of the gross primary productivity was 4.63 g 0₂/m²·d in July, while the minimum one was only 0.12 g 0₂/m²·d in December.The optimum temperature for the primary productivity was 25mC-According to the simulation experiment, the relation between primary productivity and temperature was fitted to the function;P=0.22·θ^(25-r)).The primary productivity was also affected by the available light.The maximum primary productivity occured at the half depth of the transparency generally.The relation between the primary productivity and radiation is P=0.162·(I/1.33)·exp(1-(I/1.33))+0.05.