Hydraulic components have been used in a lot of advanced machines, such as trolley, backhoe loader, shield machine and so on. A wide variety of problems appear in the use of these machines gradually, and cavitation is one of these. In this paper, the causes for the damage of hydraulic deliver motor of 312 backhoe loader used in Kulami tunnel are analyzed. The air stress in the hydraulic oil is calculated by means of formula estimation, and the stress caused by the air exploding is calculated according to related data. In the end, the damage to the hydraulic components caused by cavitation and the causes of the cavitation are analyzed.