Aiming at the problem of the phenomenon that the system performance of free space optical(FSO) communication drops sharply and the difficult problem of attenuation data acquisition in the fog environment, this paper sets up an innovative indoor FSO communication system to simulate the transmission of laser in foggy weather. The attenuation condition of FSO communication in foggy weather is studied and the channel probability model of the indoor FSO communication system is constructed. In the indoor FSO communication system, this paper simulates the 1550 nm wavelength laser under different visibility of transmission attenuation condition, analyzes the statistical characteristics of FSO signals under different visibility, chooses Gamma fitting distribution to establish channel probability model. By using intensity modulation /direct detection and on-off keying modulation method, the bit error rate of the FSO communication system under different link length、different visibility and different transmission power is deduced. The experiment verifies the feasibility of the analog channel.