Specific to synthetic aperture ladar(SAL), the impact of signal phase error on synthetic aperture imaging was analyzed. Laser signal was modeled, the impact of laser signal coherence on SAL azimuthal resolution was analyzed, one solution by delaying the local oscillator signal was proposed. The impact of nonlinear distortion in LFM signal on range resolution was analyzed. To solve the problem of the random initial phase error introduced in the process of laser LFM signal modulation and amplification, one nonlinear distortion and phase error calibration correction method based on reference channel was proposed. Experiment and simulation results are shown.