The shipborne phased array radar obtains the real-time attitude change of the radar through the strapdown inertial navigation, and the angle measurement error will be introduced when the targets are transformed to the navigation coordinate, as a result of the strapdown inertial navigation’s measurement errors. A method of angle measurement error suppression is proposed, which adjusts the heading angle deviation between the strapdown inertial navigation and the phased array radar by constructing the cost function of the joint azimuth angle measurement error and pitch angle measurement error. Afterwards the minimum comprehensive angle measurement error is obtained from the optimal installation position to realize the maximum suppression of the angle measurement error. The simulation experiments verify the effectiveness of this method.