Linear chirp laser signal is often employed as the transmitted signal of synthetic aperture laser (SAL) radar. However, actual frequency sweep properties of fiber laser always produces nonlinear terms such as quadratic and higher order terms. Existence of nonlinear terms produces phase errors during pulse time, leading to blurring of target in range direction and further reduces imaging resolution of range direction. It makes compensation of the nonlinear chirp from laser source. An algorithm of matched filtering in frequency spectrum to overcome the phase error from nonlinear chirp is developed. The results of simulation show that the image in range direction can be well compressed. At the same time, effects of signal compression in the range direction under different parameter situations, such as reference channel length as well as ratio of nonlinear contribution, are analyzed.