The design of hydrostatic supplement equipment was introduced mainly. Based on technique of high pressure and pneumatic balance, this design was applied in hydraulic closed drive steering system, and the problem of low steering precision caused by the changed pressure was resolved, which existed in the conditions of oil leakage and environmental temperature changing, and the hidden dangerdriving trouble was avoided. Using the equipment, the pressure stabilization of the hydraulic closed drive steering system is maintained, the operation is simplified and the efficiency is improved.