In order to meet the need of radar testing in the state of antenna being offline, a signal simulation system of radar antenna azimuth based on FPGA is designed. The signal simulation of radar antenna azimuth is very important for the test of radar signal processor. The PWM signal,direction control signal and braking signal of motor given by servo control system are used to compute the azimuth position of radar antenna which is processed to be simulating pulses of optical encoder sensor and outputed to radar signal processor. The simulation system has such advantages as that the attributes of input/output signal are in line with those of radar antenna and the method is simple to implement, which has been applied to the radar testing system of a certain type. Practice proves that the effect is good.