Abstract: Based on the LFM(linear frequency modulation) signal and the principle of the heterodyne, the expression of the output of the heterodyne detection in synthetic aperture ladar was induced in detail. The data image of the array target was simulated in a strip-map mode sequentially. The object image was reconstructed by the method that Fourier transform and some emendation were used in the range direction while the correlation operation was used in the azimuth direction. The analytical expression of the object image was induced in both the range direction and the azimuth direction, so that the intensity distribution of the object image were analyzed in the azimuth direction and the range direction separately. Therefore, many improving methods were advanced by analyzing the factors on the image quality, which may provide many references for further optimization.