Abstract: The effects of atmospheric scales on aperture averaging of Gaussian-Schell beam propagating in an atmospheric turbulence were examined by means of a modulation spectrum for the index of refraction fluctuations including the outer-and-inner scales of the atmospheric turbulence and the approx imation of across-spectral density function for the coherent function.An easily evaluated expression valid in the weak fluctuation regime for aperture-averag ing factor including the effects of the turbulent outer-scale was obtained.The results show that with the outer-scale reducing,the aperture averaging of scintillations for Gaussian-Schell beam propagating in an atmospheric turbulence will reduce.The effect of the outer-scale of turbulence on the aperture averaging of scintillations for incoherence beam can be ignored.