From the generalized Huygens-Fresnel principle, residual phase structure function method is used to calculate the modulation transfer function and far-field irradiance profile of a focused Gaussian beam blocked by a circular aperture through atmospheric turbulence, the Strehl ratio is a useful measure which is used here to evaluate the effects of several lower-order aberration modes corrections on the spot quality in the received plane, and the results derived here agree well with the results of correlation reference, moreover, the complexity of the new method used here is superior to the method used by correlation reference. The calculated results are analysed and discussed.