The invention discloses a wave energy power generation system and a posture adjusting device and method thereof. The posture adjusting device comprises a bearing column provided with a plug pin hole, the bearing column is sleeved with an upper flange and a middle flange, the upper flange and the middle flange are provided with a first plug pin oil cylinder and a second plug pin oil cylinder correspondingly, the middle flange is provided with a prism, the upper flange, the middle flange and the prism can vertically slide along the bearing column, the lower flange can vertically slide along the prism, a lifting coarse adjusting oil cylinder is arranged between the upper flange and the middle flange, and a lifting fine adjusting oil cylinder is arranged between the middle flange and the lower flange; the device further comprises a steering device and a hydraulic system; and the steering device comprises a hydraulic motor and a rotary bearing. The wave energy power generation system comprises a wave energy power generation device and the posture adjusting device of the wave energy power generation device. According to the posture adjusting method, the lifting coarse adjustment oil cylinder and the lifting fine adjustment oil cylinder are matched to lift the wave energy power generation device; and the hydraulic motor is adopted to drive the rotary bearing to drive the weave energy power generation device to rotate.