In order to increase the detection range of the system,IR searching system is equipped on top of a vehicle-mounted mast.As the mast is introduced,angle measurement of the system is strongly influenced.On the basis of error classification and error analysis of angle measurement,a new method based on double antenna differential GPS and attitude measurement is proposed to accomplish the evaluation of angle measurement precision for the whole system rapidly.The results show that this method can rapidly achieve the calibration of angle measurement precision,and the measuring results are in good agreement with theoretical calculation.