The presence of nonlinearity chirp in the transmitted synthetic aperture ladar (SAL) signal badly deteriorates the range resolution. The signal model with nonlinearity chirp is established in this paper, by which the pair-echo effect induced by the nonlinearity term is analyzed. By estimating the nonlinearity chirp using the time-shift characteristic of the Fourier transform, a novel modified frequency scaling algorithm is proposed to correct the ladar nonlinearity based on the residual visual phase filter. Through simulation experiments, the modified algorithm confirms its superiority in terms of resolution and image quality.