The causes for the common malfunctions of the main hydraulic system of Lovat shield machines are analyzed. Technical measures to reform the main hydraulic systems of these shield machines, including the design of the hydraulic system, the calculation of the pressure loss in the hydraulic hoses, the assembly and debugging of the components of the hydraulic system after reforming, are determined. After the reform, the malfunctions of the main hydraulic system are solved and the design of the hydraulic system of the main hydraulic oil tank is improved. 