For the permanent magnet direct drive wind generator, the volume and weight of the motor have a great influence. As far as the general rule is concerned, no matter what kind of electromechanical device, if the volume, weight or speed is very large, it will inevitably cause a series of mechanical problems. In this paper, the mechanical mechanism design of generator is chosen as the research direction to solve the lightweight problem of generator. Therefore, in this paper, the author first introduces the overall structure of permanent magnet direct drive wind generator. After that, the structure of the motor is designed with light weight from the motor parts, which partly reduces the weight of the motor. Then, a structure to resist stator deformation is designed in this paper. By directly installing a certain number of double-head bolts on the base and shell to increase the radial strength, the electromagnetic force and gravity are offset while the strength of the motor base is strengthened, and the weight of the motor is reduced effectively. Finally, three kinds of structures are selected by the control variable method. The analysis results show that the optimised structure has better anti-deformation effect and better strength effect than that of increasing plate thickness. The new anti-stator deformation structure not only solves the problem of overweight problem of the motor base, but also strengthens the strength of the frame and prevents it from deforming.