The coupling efficiency theory model of the spatial light into few-mode fiber in the different influence factor is established. Takes two-mode fiber for example to study the relative aperture effect on coupling efficiency. When the relative aperture is 0.17, the highest coupling efficiency is 82.96%. The coupling efficiency in the presence of tilt, defocus and random angular jitter is studied, the experiment show that when the lateral offset is 4 μm, the coupling efficiency of two-mode fiber is higher than single-mode fiber about 10.23%, when the axial offset is 125 μm, the coupling efficiency of two-mode fiber is higher than single-mode fiber about 11.24%, when the random jitter amplitude is 5 μm, the coupling efficiency of two-mode fiber is higher than single-mode fiber about 12.1%. Accordingly, the few-mode fiber can inhibit interference factor such as tilt, defocus and random angular jitter when the signal reception.