Abstract: Image quality of azimuth multi-channel SAR is influenced by such factors as system parameters, array errors, and signal processing strategies. The image quality of azimuth multi-channel SAR is studied deeply. Firstly, the signal model is improved. The introduction of the reconstruction coefficient provides more flexibility for designing the reconstruction network. In the frame of digital beam-forming, a series of reconstruction algorithms are then discussed for signal reconstruction. Secondly, based on the power spectrum of the reconstruction error, the analytical expressions of output Signal to Noise Ratio (SNR) and Azimuth Ambiguity to Signal Ratio (AASR) are deduced. Thirdly, the performance of the reconstruction algorithms is assessed quantitatively. Simulation experiment results confirm the validity of the theoretical analysis. Theoretical results provide technique support to system design, signal processing and image quality evaluation of azimuth multi-channel SAR.