Abstract: A two-stage planetary one-stage parallel gearbox of a 5 MW offshore wind turbine is taken as the research object. 16 sets of orthogonal experimental tests are established and simulated within the virtual prototype software Simpack,in which the helix angles（ A,B,C）in different stages are independent variables whose values are 5°,8°,11°,15°,respectively. The even load and vibration characteristic under each factor and level is evaluated and the validity of the orthogonal simulation results is verified. The results show that the even load characteristic of the planetary is mainly related to the helix angle of its stage and affected by helix angles in other stages. In general,the larger the helix angle,the better the even load characteristics. The main factor that affects the vibration signal of the rear bearing position of the high-speed output shaft is C,and when the value of C is 8°,the vibration signal is the weakest. The research results provide theoretical support for the meticulous design of the helix angles of large offshore wind turbines.