Multi-channel SAR technique is an effective solution to obtain high-resolution images with better than 0.1 m. A radar transceiver channel scheme which consists of one wideband transmit channel and 8 down-converter receive channels is designed and implemented in an airborne SAR system. According to the frame design of the transceiver channel, this paper focuses on proposing one solution for obtaining and calibrating the real system amplitude-phase errors accurately. A closed-loop space radiation method is used to extract amplitude-phase errors of the broadband transceiver unit and a frequency-offset error correction technique is used to extract the sub-channel amplitude-phase errors in multi-channel receiver unit. Then the combination of the two is used to compensate the entire system error which will impact bandwidth synthesis and image processing seriously. An acute test and analysis of the system error is performed. The final airborne experiments demonstrate the validity and feasibility of the system calibration.