The hydraulic control system of the diamond wire saw which consists of two types of valves has been established considering the underwater work circumstances. The frogmen can control the start-stop or reversing of diamond string bead wires by using the manual reversing valve and adjust its rotate velocity of radial feed motor by using the governor valve conveniently. It belongs to an open-loop control system with the advantages of simplicity and reliability and disadvantages such as low automation level, low control accuracy, great labor intensity and adjustment of control parameters by means of detection system, sensors or instruments. Then the close-loop control system of radial feed and the velocity control model of hydraulic servo-valve system have been established based on the reasonable process parameters obtained by cutting experiments of the diamond wire saw.