This paper analyzed the principle of method which adjusts the phase between sum and diff channel quickly. An antenna with 18 m diameter is discussed as an example, it is proved that the lobe of large aperture antenna is narrower under X band relative to the S band, illustrates a higher pointing accuracy is necessary when using X band space target as the electric signal source to complete quickly phase adjust which can make sure that the target is still in the main beam after offsetting the electric axis. By analyzing the pointing error source and model of the parabolic antenna, a method is put forward based on angle pointing error model and to correct angle using offset which calculated by angle measuring error parameters, can significantly improve the antenna electrical axis pointing accuracy for target, so as to ensure the large aperture antenna for X band target of quickly phase adjust success rate. This method has been verified in engineering effectively.