A heterogeneous spherical microalgae model was established, and for the first time, the optical constants of microalgae components were used to characterize the optical constants of microalgae cell microstructure. The radiation characteristics of the heterogeneous model were calculated using the multi sphere T-matrix method. The radiation characteristics of Chlorella vulgaris were measured to verify the theoretical calculations. Compared with the homogeneous sphere model based on the equivalent medium theory, the calculation accuracy of the heterogeneous model considering internal microstructure has been improved by 16% in the spectral range of 400∼750 nm, and the scattering phase function is closer to the experimental results. In addition, when determining the optical constants of the model microstructure based on the composition of microalgae, the accuracy of the theoretical calculation of radiation characteristics is much higher than that of microalgae models that use fixed values as optical constants.