The invention discloses a hydraulic control system of a gearbox. The hydraulic control system comprises an oil supply system, a gear control system, a clutch control system and a TCU (Transmission Control Unit) controller, wherein the oil supply system comprises an energy storage and a first pressure sensor which is used for detecting oil pressure in the energy storage; the gear control system comprises a first pressure valve, a second pressure valve, a first reversing valve, a second reversing valve and a third reversing valve, and oil liquid passes through the first or second pressure valve, the third reversing valve and the first or second reversing valve in sequence and then enters a set gear piston cavity; the clutch control system comprises a third pressure valve, a fourth pressure valve and a selector valve, and the oil liquid passes through the selector valve and the third or fourth pressure valve in sequence and then flows into a set clutch piston cavity; and the TCU controller is electrically connected with a motor, all electromagnetic valves and a sensor. According to the hydraulic control system of the gearbox, no matter which signal is input, no more than one gear and one clutch can be engaged, additionally, intermittent operation of an oil pump can be realized, and power loss is reduced.