The working station can not be obtained directly while the cutting equipment operates under water. In original operator，the speed of cutting operations was estimated by the flow quantity of hydraulic motor. Obviously it has a high distortion and low response speed. To improve the precision of speed detection, a deepwater encoder, which was used to detect the speed, and a proportional flow valve, which was used to adjust the traffic speed of hydraulic motor,were employed to achieve realtime and accurate control of speed. The control strategy proposed was realized by using a programmable logic controller.