Abstract: The received laser beam in a free-space optical communication using fiber-optic components system must be coupled into a single-mode fiber. However, atmospheric turbulence degrades the fiber-coupling efficiency. Adaptive optics can reduce the effects of atmospheric turbulence and improve fiber coupling efficiency. According to space light into single-mode fiber coupling efficiency expression with the atmospheric turbulence parameters, the single-mode fiber coupling efficiency expressions based on adaptive optics correction was deduced. Simulation results show that adaptive optics system correcting the aberrations induced by turbulence can increase the spatial coherence radius and then can improve the coupling efficiency. The the relationship between Strehl ratio and coupling efficiency was studied. The results show that regardless of the presence or absence of adaptive optics correction, both have good fitting relationship. Therefore, simple Strehl ratio can be used to estimate the single-mode fiber coupling efficiency.