The basic working principle and design characteristics of the hydraulic system of the coil box were described. In light of onsite application, the problems,including unimproved cooling system during system capacity expansion when the system was in use, unclean “clean” water circulating system, unreasonable PLC logic control, system heating caused by blocked oil discharge of pump, malfunction of the system caused by design defects and improper choice of components, were proposed. Accordingly, the measures including improving circulating cooling system, adding inflow filter, improving PLC logic control to improve system heating, correcting hydraulic circuit, reselecting hydraulic components were put forward to optimize hydraulic circuit with satisfactory results.It provides reference for the design, installation, maintenance and management of similar devices in the future.