Abstract: Described here in the paper is the working principle of the mobile stand locking mechanism of the steel pipe hydrostatic testing machine. The main reason for the frequently-happening fault of stuck of the said locking mechanism is identified via analysis, i.e., the abrasive wear of the mechanism’s pin device due to long term service. Owing to the substitution of the integrated hydraulic cylinder for the pin device, the negative influence by the mechanical wear amount and the gap amount as staying with the said pin device is completely eliminated, and thus the failure rate of the mobile stand locking mechanism of the hydrostatic testing machine is reduced to zero, and as a result the operation efficiency is enhanced, while the intensity and cost of the maintenance are also reduced.