Monopulse radar is widely used for its high-precision angle measurement and powerful anti-jamming performance. Because the components of radar system are not ideal, the radar measurement accuracy is reduced. According to the structure of sum and difference patterns phase-comparison two-dimension monopulse radar system, the system is divided into three parts, which include the circuit from antenna to sum-difference comparators, the sum-difference comparators and the channel signal processing module. The impacts of their non-ideal to the performance of angle measurement are analyzed and simulated. Some meaningful conclusions are acquired which may bring great convenience to engineering and system design.