Although the conventional design can meet the requirements of transmission function, the design scheme is not the optimal design scheme when considering the economy and safety. It can not meet the requirements of minimizing the tractor volume and mass at the same time, and the tooth profile of the gear transmission system can withstand greater impact and tooth wear optimization. Therefore, it is of great practical significance to make full use of different constraints and computer-aided technology to optimize the design scheme.

1) With the support of computer-aided technology, the optimal design of planetary gear transmission system is carried out by using the optimal design method. Under the condition of meeting the requirements of strength and structure, the optimal design of structure is achieved.

2) The dynamic model of tractor planetary gear transmission system is established, and the influence of the comprehensive error in the meshing process of the gear pair and the time-varying meshing stiffness of the ulnar clearance is considered.

3) The time-varying meshing stiffness of gear pair is expressed by Fourier series, and the meshing stiffness of planetary gear under different fault degrees is derived.

After the completion of the structure design, in order to further obtain the meshing stiffness of the planetary gear transmission system, the concept of gear pair meshing comprehensive error and backlash caused by the design and processing in the process of gear meshing is introduced, and the mathematical model of the planetary gear transmission system is established in the field of transmission system dynamics; Considering the time-varying effect of vibration transmission path on vibration signal, the mathematical model of meshing stiffness of planetary gear transmission in fault mode is deduced, and the meshing stiffness under different fault degrees is obtained, which provides reference for fault monitoring of tractor planetary transmission system.