Bit error rate (BER) performances of DPSK are researched for space uplink optical communication system. Considering further phase fluctuation effect based on the traditional atmospheric turbulence model, BER performance versus transmission power, zenith angle, frequency deviation, divergence angle and transmission diameter are discussed for different wavelengths. Simulations, especially, indicate that considering the phase fluctuation effect, BER performance is sensitive for low frequency deviation. It also confirms that wavelength of 1550nm on communication system is still a good choice for the better BER performance. This work is helpful for enhancing transmission quality and the design of space optical communication system.