The helix line modification of pinion is determined by the analysis of the deformation of the pinion,through the mathematical modeling of gear dynamics,a theoretical basis for transmission error is provided.The gear modification of output gear of a 2 MW wind turbine gearbox is carried out. The tooth profile modification of gear pair is carried out by using the KISSsoft software. The model of a 2 MW wind turbine gearbox is built by MASTA software. The pinion helix line modification is designed according to the deformation of pinion and the related formula. According to the simulation analysis of wind power gearbox,the load distribution and transmission error of the gear before and after modification are compared. According to the testing of a 2 MW wind turbine gearbox,the vibration speed of the output end and the gear meshing situation under each working condition are researched and analyzed,the rationality of modification is determined.