The performance of wireless laser communication can be affected due to atmospheric turbulence and the aperture averaging can effectively inhibit scintillation caused by turbulence. The aperture averaging factor of scintillation for Gaussian-Schell mode (GSM) beams is derived according to the expression of aperture averaging factor given by Tatarskii and the relationship between mutual coherent function and cross-spectral density function for narrow-band wavefield. The effects of coherent parameter of the source,the strength of turbulence, inner scale and outer scale of the turbulence on the aperture averaging factor of scintillation for GSM beams are discussed. It is shown that the effects of the coherent parameter on the aperture averaging factor become smaller with the turbulence increase. The aperture averaging factor reaches saturated more quickly with stronger turbulence, and further increasing of the aperture of receiver becomes no longer valid in reduction of scintillation. The inner scale of turbulence has a significant effect on aperture averaging factor，while the influence of outer scale can be neglected. The inner scale of turbulence plays an important part in analysis of scintillation.