Abstract: The natural frequencies and modes of the first six modes are extracted from the modal analysis of a transmission gearbox, and the influence of each mode on the performance of the transmission box is analyzed. The first natural frequency is very close to the excitation frequency produced by the gear transmission components at the end of the transmission box, which is easy to cause vibration. Through the analysis of the load flow of the transmission box, the position of the internal ribs is optimized, so that the first natural frequency is greatly increased, the amplitude is reduced, and the dynamic stiffness of the transmission box is improved.