The invention discloses an underwater robot movement posture adjusting device and method. The underwater robot movement posture adjusting device comprises a base, a supporting seat, a balancing mechanism, a rotating table, a bearing table, a barycenter trimming mechanism, a plurality of load blocks and a control mechanism, wherein the bearing table is arranged at the telescopic ends of three telescopic mechanisms, the barycenter trimming mechanism is arranged at the top of the bearing mechanism and is provided with a slide block, the slide block is provided with a lifting mechanism, the load blocks are arranged at the upper end of the bearing table in a slide mode and are erected at the upper end of the barycenter trimming mechanism, a penetrating hole is formed in the center of each loadblock in a penetrating mode, the inner diameter of each penetrating hole is no less than the outer diameter of the lifting end of the lifting mechanism, the lifting end of the lifting mechanism extends into the penetrating holes in a selective mode, and the control mechanism is correspondingly connected with the telescopic mechanisms and the barycenter trimming mechanism. The barycenter and postures of a robot can be adjusted actively to meet working requirements of the robot, and the technical problem of posture adjusting difficulty of an underwater robot is solved.