Nonlinear degradation and its compensation on range resolution in synthetic aperture ladar imaging experiment caused by nonlinear frequency modulation in the transmitting laser source are investigated in detail.Theoretical discussion is carried out on the frequency broadening in the heterodyne detection signal and its influence on the degradation of range resolution due to the use of linear wavelength sweeping laser source instead of linear frequency sweeping laser source.Two compensation methods utilizing matched reference channel or mismatched reference channel are compared.Numerical simulations on degraded or corrected range images are given.An experimental demonstration using 1.55 μm tunable fiber laser system is setup and results on degradation and compensation are obtained.