Based on noise characteristics of wireless optical communication, atmospheric channel model was founded. Homomorphism filtering technology was applied to four frequency shift keying(4FSK) modulated signal denoising for atmospheric turbulence. Zero-phase digital filter in homomorphism system is desired. When the length of source code was 500 and the signal to noise ratio was 10 dB, the denoising 4FSK signal was demodulated by the zero crossing detection method, and the bit error rate arrived at 7×10-4 with turbulence parameter σ2s=0.1. The simulation results show that homomorphism filtering could reduce multiplicative noise more effectively than the traditional digital filter, and could control atmospheric turbulence to improve relibility of optical communication.