According to the study of the pimary production and light in Meiliang Bay Taihu Lake in May, October, December of 1998, August of 1999 and July, September of 2001, the anthorvS found thal the greatest primary production was at the depth of 0.2cm, the relationship between primary production(P) and the concentration of Chla was;p=0.012~0.028 [Chla] (n=30).On the basis of the relationship between light spectrum and concentration of Chla, as well as the relationship between primary production and light intensity, the relationship between primary production and light spectrum was found and validated.Further analysis revealed that the K_d of light spectrum at the blue end and at the red end was greater than that of green, the lowest was at 550 nm.