Abstract: In spherical near-field measurements of phased array antennas, the relatively large truncation errors can be caused by finite scan sphere and the beam scanning of phased array antennas. In order to solve the above problem, the weighted process method of the near-field data by the cosine window function with the parameters optimized by genetic algorithm(GA) is presented to effectively reduce truncation errors. With the rectangular planar array made up of half-wavelength dipole as the antenna under test, the spherical near-field measurements of phased array antennas are studied by computer simulation. The simulation results show that the truncation errors caused by finite scan sphere as the beam of the phased array antenna scans can be greatly reduced by processing the near-field data with cosine window function and optimizing the parameters with GA, which proves the correctness and validity of the method presented in this paper.