The invention discloses an underwater valve group prying tool. The underwater valve group prying tool comprises a valve group base (1) and a valve group (5); the valve group base (1) is provided with a sliding platform (4) capable of moving vertically; the sliding platform (4) is provided with a transverse-moving mounting board (9); the valve group (5) is arranged on the mounting board (9) in a longitudinal moving mode; the valve group base (1) is provided with a guide framework (7); a linear type guide channel is formed in the lower portion of the guide framework (7); valve group flanges (8) of the valve group (5) are arranged at the first end of the linear type guide channel in a penetrating mode; and the axes of the valve group flanges (8) are parallel to the linear type guide channel. The invention further discloses a mounting method for direct connection of the underwater valve group prying tool and a sea pipe. The method can achieve direct connection of the valve group and the sea pipe, operation is easy and efficient, only one pair of flanges is needed, potential leakage points are decreased, and safety of sea pipe connection is improved.