Abstract: For the purpose of improving range resolution of SAR system, one of the main technical approaches is to increase the signal bandwidth by means of multi-channel synthesis. Considering the issue of phase mismatch among multi-channels, channel phase error estimation and compensation method based on echo data is proposed in this paper. Firstly, the polynomial model for channel phase error is established and high-order inner-channel error is then estimated and compensated. Secondly, the residual low-order inter-channel phase error is then estimated and compensated in the procedure of multi-channel synthesis. Aiming to optimize the focus effect of compressed pulse, the optimization estimation model for channel phase error is established. According to the actual case of multi-channel synthesis, the method decomposes the procedure of error estimation and compensation and only a few echo data are required for the data process in addition, which results in the advantage of high efficiency and fast convergence speed. The effectiveness is validated by the process and analysis of real eight-channel raw data.