Microwave landing navigation system is used for UAV reducing the number of phased array scanning antenna to improve its maneuverability, by so doing, this makes scanning beam wide and main-beam's symmetry worse. The phenomenon can reduce the scanning beam pointing accuracy and robustness of original phasing methods, and consequently weaken the navigation ability. Aimed at the problem, a new method of the combined circlephase method with the improved genetic algorithm is proposed to improve the scanning beam pointing accuracy. At every scanning pointing, whenever a circlephase constant is added, the genetic algorithm is improved to optimize, determine the final phase shifters' input values and quantization manners, and overcome the shortage of circlephase method and basic genetic algorithm in using alone. The simulation shows that the beam pointing accuracy produced by the combination method is superior to the beam pointing accuracy produced by random phasing methods and basic genetic algorithm.