First,transmission equation of the laser transmitting through atmospheric turbulence channel was analyzed,ignoring other noises in the system,atmosphere turbulence was the only cause for Bit Error Rate(BER).Then,the amplitude variance and intensity variance of the laser signal were discussed,and the relationship betwwen BER and the laser communication system was deduced.The result indicated that in the weak variance condition intensity variance should be below 0.67 for communication system with BER below 10 -9;with turbulence intensity C2_n increasing,BER increased rapidly;adopting laser with longest wave to communicate can decrease BER effecively.