In the space optical communication system, the laser transmission in the atmosphere is easily affected by the turbulence effect, and the single-mode fiber with a minimal mode field radius is frequently used at the receiving end for space optical coupling, resulting in a reduction in fiber coupling efficiency and a decrease in communication system performance. To improve the fiber coupling efficiency of the receiving end, the stochastic parallel gradient descent (SPGD) algorithm and the few-mode fiber coupling demultiplexing system are combined to compensate for the wavefront phase distortion caused by the dynamic turbulence. The numerical simulation of the space optical communication with the transmission distance of 5 km is achieved. The simulation results demonstrate that the coupling efficiency of two-mode fiber is 0.5 dB-1.5 dB greater than that of single-mode fiber without SPGD algorithm correction under various turbulence intensity and wind speed circumstances. The relative standard deviation is lowered by 0.03-0.4. After the SPGD algorithm correction, the coupling efficiency of two-mode fiber is improved by 0.4 dB-2.2 dB compared with that of single-mode fiber. The relative standard deviation is reduced by 0.1-0.2 under moderate and strong turbulence conditions. Consequently, using few-mode fiber for coupling in space optical communications has a better coupling effect than using single-mode fiber, which improves the communication system’s stability.