：Most present researches of FSO system are based on the assumption of plane wave or spherical wave,while the actual transmitting beam of FSO system is Gaussian beam,so the study of the effect of different transmitting beam on the performance of FSO system is important.Starting from the aperture averaging effect,without considering the impact of the turbulent inner and outer scale,the effect of turbulent strength on the aperture averaging effect is analyzed under the Gaussian beam condition.It′s shown that the aperture averaging effect is more obvious by increasing the turbulent strength.And then,under the weak turbulent condition,the effect of transmitting beam on the improvement of BER performance by aperture averaging effect is simulated.The results show that Gaussian-beam wave has the most apparent impact on BER performance,and saturation occurs first,followed by spherical wave.Plane wave is relatively gentle.