The planetary carrier and shaft system in the gearbox which was used in the megawatt class wind turbines was studied by finite element method. Considering the interference fit and loading on planetary shaft, the stress and deformation distributions of planetary carrier and shaft system under the rating condition were investigated. Then the structure of planetary carrier was optimized with the purpose of less weight. Finally, the improved structure of both the junction plate and planetary shaft with openings is reasonable by the use of CAE technology, which is about 12% lighter comparing to the original structure. The results provide reference for the design and practical application of planetary carrier and shaft system.