The design and realization of a 7-Function master-slave deep-sea hydraulic manipulator can be used in 7000 meters depth is proposed. Linear actuator, rotary actuator and cycloid motor are the three basic modules of the slave arm. To achieve smooth control result, PI control algorithm with variable gains is applied on the control of the slave arm. The control algorithm is also certified effective in alleviating the movement delay and overshoot jitter of slave-arm. Based on the reliable running experiments on land, a pressure experiment system to test the manipulator’s index of 7000m depth is proposed. The pressure experimenting process is described in detail. Finally, actually application testing in the sea is presented. During the process of application testing, the manipulator movement function was normal and successfully completed the goal underwater fetching tasks. The whole result of experiment shows that the hydraulic manipulator satisfies 7000m design depth index.