For the problem of the big errors in the calculation of atmospheric attenuation under water fog weather, starting from the physical phenomena of water fogs weather, through the revision of the existing model, a more precise and reasonable model was proposed. And using the proposed model, the performance of free space optical (FSO) communication system was analyzed, the simulated results pointed out that the relative errors caused by the existing model can′t be ignored. The work can provide a theoretical basis for the evaluation and estimation of FSO communication system and other related domain in water fogs weather.