For free-space optical communication systems using the technologies of fiber-optic communication,the received beam must be coupled into the single-mode fiber(SMF)first.However,the random angular jitter existed in receive terminal leads to a dramatically decrease of coupling efficiency and deteriorates the communication performance.In this paper,we expound the theory of coupling the incident beam into SMF,and analyze the effect of the random angular jitter on coupling efficiency.On this basis,in order to improve the coupling efficiency,we propose to utilize the raster spiral scan and stochastic parallel gradient descent(SPGD)algorithm to compensate the influence of the random angular jitter.