At present, there are two models applied in the study at home and abroad in an attenuation model of rain transmisson, which are scattering model and shading effect model. However, the shading effect model has a theoretical defect in dealing with large-sized raindrops located near the laser field of view, and the scattering model requires an enormous amount of computation caused by the multi-scattering problem at the far end of the field of view. This paper presented an improved algorithm for the raindrop attenuation model which was based on projected area of raindrops at receiver. The algorithm corrected the case when a single raindrop was obscured within the viewing angle of the receiving lens. The model was simulated by MATLAB, and the attenuation correlation curves of the improved attenuation model, the scattering model and the shading effect model were obtained. Finally, the accuracy of the improved algorithm was verified by the natural rain field experiment. The results show that compared with the shading effect model, the accuracy of improved model is improved by 54.6% when the transmission distance is 100 m and the rainfall rate is 1.2 mm/h. It is shown that the improved algorithm can improve the accuracy of the raindrop attenuation model. The research of the project provides a theoretical support for the development of the blue green laser atmospheric communication detection technology.