Abstract: Attitude adjustment is the key to determine the operation capability and motion stability of underwater robots. For this purpose, an integrated system of ups and downs and attitude adjustment based on all-water hydraulics is proposed for the underwater inspection robot of coal mine pumped storage power station. The system is mainly composed of attitude piston cylinder, variable pump and special six-position six-way control valve which are symmetrically arranged on both sides of the robot. The transmission medium comes from the external water environment of the robot, and it has four adjustment states:ups and downs, trim, lateral and diagonal roll. The ups and downs adjustment is a mass exchange process between the robot and the external water, and the exchange channel between the robot and the external water is closed when adjusting the attitude, which can ensure that the robot is always in a hovering state during the attitude adjustment process and improve the stability of the robot attitude adjustment process. On the basis of structural innovation, the robot’s center of gravity and attitude angle equations are deduced, the AMESim simulation model of its attitude adjustment is established. The process of robot’s ups, downs and attitude adjustment is analyzed, and the influence of total length, spacing, diameter of piston cylinder and z coordinate of floating center on the attitude angle is studied. The results show that increasing the diameter of piston cylinder, the z-coordinate of floating center, the total length of piston-cylinder and the distance between the piston and cylinder are helpful to improve the sensitivity of attitude angle adjustment. The more obvious its effect on the attitude angle, the larger the cylinder diameter, the smaller the effect on the longitudinal attitude angle, while the total length of the piston cylinder only affects the longitudinal attitude angle, and the distance between the cylinders only affects the transverse attitude angle. After optimization, the maximum longitudinal attitude angle and transverse attitude angle of the robot can reach 78.46° and 68.20°, respectively. The proposed integrated system of ups and downs and attitude adjustment based on all-water hydraulic has many advantages such as compact structure, convenient regulation, energy saving and environmental protection, etc. The research results laid theoretical foundation for the subsequent development of sinking floating and attitude regulation system