In order to explore the impact of atmospheric disturbances on the performance of wireless optical communication （WOC） systems, the Mie scattering model is used to deeply analyze the attenuation of scattered light in rain. First, the correlation function of the raindrop terminal velocity fluctuations is solved, and then the Wiener-Khinchin theorem is applied to calculate the power spectrum of the scattered light. A method combining Marshall-Palmer distribution with multiple raindrop terminal velocity models is creatively proposed to reveal the specific impact of raindrop terminal velocity on the received light intensity spectrum. The simulation results show that, under the same distribution of raindrop terminal velocity, as the rainfall rate increases, the attenuation of the scattered light spectrum of the four raindrop terminal velocity models also increases, but the shape of the spectrum remains basically unchanged, the attenuation of the beacon light with a wavelength of 532 nm is about 1 dB more than that of the signal light with a wavelength of 1 550 nm.