In order to thoroughly understand the characteristics of the temporal spectrum of atmospheric scintillation and provide references for engineering design and performance evaluation of the optics system employed in the atmosphere, the generally analytic expression of the atmosphere scintillation power spectrum was theoretically deduced and the frequency domain characteristics of atmospheric scintillation under different propagation conditions was numerically investigated. For horizontal path with an aperture receiver, in the high frequency area, the scintillation power spectrum of the plane wave obeys the power law with an exponent of -17/3, while the scintillation power spectrum of the spherical wave obeys the power law with an exponent of -11/3; for the whole layer downlink path, the scintillation power spectra obey the power law with an exponent of -17/3 in the high frequency area, and there is a slow transformation area between the low frequency area and the high frequency area. The larger the aperture becomes, the wider the slow transformation area grows; besides the frequency spectrum width of the low frequency area and the slow transformation area is about 150 Hz under typical atmosphere conditions for plane wave.