This chapter is mainly about the design and calculation of semi-axle, which is connected with driving wheels. Although the structure of semi-axle is not very complicated, it can even be said to be very simple, but without semi-axle, the vehicle may not be able to drive. Therefore, the function of semi-axle is very great. This design mainly adopts full floating semi-axle. During the design and calculation of full floating semi-axle, several possible load conditions are emphasized, and the calculation is carried out in view of the situation without lateral force.