The bit error rate (BER) at different atmospheric turbulence conditions is analyzed, which illustrates the adverse affection of wave-front aberration caused by atmospheric turbulence on binary phase shift keying（BPSK） coherent optical communication system. Atmospheric turbulence aberration can act on optical communication system, which leads to bit error and is independent of system signal-to-noise ratio (SNR). Simulation results note that bit error is prone to emerge in the case of infinite SNR, when the peak-to-valley (PV) value of wave-front of received optical signal is greater than one wavelength. And the PV value of wave-front is strictly required with the decreasing of SNR. In addition, coherent mixing efficiency decreases rapidly, which is caused by the intensity fluctuation and phase aberration, consequently, resulting in the system bit error rate increasing.