The gearbox is a very important part of the vehicle, which can change the gear ratio and increase the torque and speed of the drive wheel. With the development of modern technology, the gearbox has also been upgraded. From the original manual transmission to the now continuously variable transmission, from no synchronizer to having a synchronizer, the control is more and more convenient. At present, diesel engines are widely used in construction machinery, and the range of torque and speed change is small, which cannot meet the requirements of traction force and running speed of vehicles under various working conditions. Gearboxes are needed to solve this contradiction. The performance of the gearbox is the key to measuring the dynamics, economy and drivability of construction machinery. The current shifting systems mainly include: mechanical transmission, hydraulic transmission, and hydrostatic transmission. The gearbox has manual shifting and power shifting, and the structure is fixed-axis and planetary.