In order to improve the accuracy of ground angle guiding equipment in Microwave Landing System，based on microwave linear phased array antenna theory, the main factors of causing phased array antenna beam to point error and the errors produced by floor phase feeding in different Quantization steps are analyzed. Beam pointing errors obtained from floor phase feeding and from randomizing phase feeding by using 4-bit Phase Shifter are compared. Through simulation, two randomizing phase feeding methods are particularly discussed and analyzed. The periodic error is eliminated by using these two methods and consequently the phased array antenna beam pointing accuracy is improved especially by Appropriate Random Phase Quantization. The simulation results indicate that beam pointing error is significantly decreased and the location accuracy is greatly improved.