The atmospheric environment seriously affects performance of the free space optical communication system. Considering the influence of weather environment, atmospheric turbulence and directivity error on laser communication, we establish a joint channel statistical model, and derive the performance parameters of free space optical communication system based on on-off keying modulation, such as average bit error rate, average channel capacity and outage probability and their closed expressions, using Meijer-G function. The performance parameters of the system are simulated and analyzed under different M turbulences, different normalized pointing errors and visibilities of 5 km and 20 km. The results show that the smaller the directivity error, the greater the influence of turbulence on the performance parameters of the communication systems; the bigger the directivity error, the more likely for a best beam divergence angle existing to make the communication system achieve the best performance.