We study the statistics of scintillation at the airborne receiver for space earth space link by analysed the modulatory mechanism of atmospheric turbulence and terrain scattering on propagating laser beam. The scintillational statistics are governed by the joine effects of atmospheric turbulence and terrain scattering (such as terrain, sea and forest). The probability density functions of scintillation for the terrain, the sea surface and the forest, the two scattering terrain model was obtained, in which the probability integral is made by the method of steepest descent. The joine distribution of geneval Chi-Squared distribution for scattering terrain and atmospheric turbulance is found flatten markedly and its peak shifts to the low end of normalized irradiance.