Abstract: The channel mismatch error between separate radar instruments is one of the challenges in the single pass Interferometric SAR (InSAR) system. A channel amplitude and phase mismatch error model is introduced. The correlation coefficient with the channel mismatch error is obtained by a statistical signal model of extended scene. The influence of channel mismatch error on the InSAR phase deviation and variance is analyzed. Finally, a ground-based hardware-in-loop simulation is carried out to study the actual radar channel mismatch error impact on the InSAR performance. The simulation results are concordant with the theoretical analysis, which validate the correctness of the influence analysis of the channel mismatch error.