The state of primary production in a lake is greatly affected by the optical conditions in the water, and closely related to the euphotic depth Zcu, The apparent optical parameters such as Zcu depend on the transferring of solar radiation in vvatcr, consequently, on the optical coefficients of water body such as absorptance aud scattering. In this paper, the field data of suspended materials in Taihu Lake are used for computing of inherent optical parameters of the lake. With the computed results, a numerical model is developed to study the transferring of solar radiation in the lake in which the concentration of suspended materials is considered to be variable vertically. Using this model the factors which influence on the transferring of radiation in the water are discussed.