We assume that the measurement errors of absorption coefficient and remote sensing reflectance are zero in October 2004, Lake Taihu. Then we can employ the optimization algorithm to simulate the backscattering coefficient by the most appropriate bio-optical model especially in the optically deep waters, where the bottom has no influence on remote sensing reflectance. Finally, the possibly real backscattering probability of suspended particulate matter may be approximately calculated by the quantitative relationship between the tested backscattering probabilities and their corresponding backscattering coefficients of suspended particulate matter. The results show that the backscattering probability of suspended particulate matter is not a constant and can be expressed as a quadratic function of wavelength, and the values are 0.017, 0.017, 0.027, 0.033, 0.054 and 0.094 at 442, 488, 532, 589, 676 and 852 nm, respectively; with a mean of 0.041±0.030.