The invention relates to an underwater valve actuating mechanism comprising a housing, a drive system, a redundant drive system, a rotary movement converting system and an underwater robot operating system. The drive system comprises a servo motor, a reducer, an overrunning clutch, an electromagnetic clutch and a gear shaft; the redundant drive system comprises another servo motor, another reducer, another overrunning clutch, another electromagnetic clutch and another gear shaft; the rotary movement converting system comprises two small gear, a large gear, a screw shaft, a nut, a hook cylinder, a joint and a spring; the underwater robot operating system comprises a cylindrical support, a trapezoidal screw, a trapezoidal nut, an underwater robot joint, an underwater robot interface, a pushing and pressing plate and a plurality of pushing and pulling rods. The underwater valve actuating mechanism can be controlled all electrically, higher safety during operation in deep-water environment is guaranteed, the functions of urgent reply, redundant drive design, valve switching state display, inner and outer pressure balance and underwater robot fault operation are provided, and the high application value is provided.