The radar attitude determination system is actually an inertial navigation system. If it is not calibrated for a long time, the zero position of the accelerometer will change, which will directly affect the accuracy of horizontal measurement. In order to solve this problem, this paper analyzes the system error mechanism and observability. According to the actual radar antenna motion range, a zero reference error compensation scheme of accelerometer without disassembly is proposed. The calibration method is simple and can effectively identify and estimate the zero error of three-axis accelerometer, and the dynamic horizontal reference accuracy after compensation is improved from 2′ to 0.5′, which is especially suitable for large equipment such as radar trucks that are inconvenient to disassemble.