For free-space optical communication systems, spatial light must be efficiently coupled into the single-mode fiber first. However, the initial alignment error and the random lateral deviation existed between focused spot and single-mode fiber lead to a dramatic coupling loss. A theoretical model of coupling the spatial light into single-mode fiber is expounded, and the effects of the lateral deviation and the random jitter on coupling efficiency are analyzed. On this basis, in order to improve the fiber coupling efficiency, a coupling scheme based on raster spiral scanning algorithm and stochastic parallel gradient descent (SPGD) algorithm is proposed. Simulations on the process of error correction and the improvement of coupling efficiency after error correction are carried out. The results show that, by setting the optimal scanning step, the initial alignment error can be efficiently corrected by raster spiral scanning algorithm, the success probability of initial alignment error correction can be higher than 99%. The residual initial alignment error focuses in 0.5-0.6 μm, and the coupling efficiency has been improved perliminarily. By adopting the SPGD algorithm, the random lateral deviation between focused spot and single-mode fiber can be corrected, and the coupling efficiency also rises to 0.81, which approaches the theoretical limit without turbulence. After the correction, the coupling efficiency is significantly improved.