The invention discloses a valve watertightness pressing test device, and provides a structure capable of bidirectionally performing a watertightness pressing test. When the device is used, a motor is started, the motor drives a lead screw to rotate, the lead screw drives a threaded connection block, thereby driving a lower ejecting plate to move towards an outer side, a hoisting mechanism is utilized to flatly place a large valve on a lower ejecting block, the motor is driven to rotate reversely to move the top ejecting plate back to an original position, a cylinder is driven to enable an upper pressing plate to press downwards, thereby enabling the upper pressing plate to be connected with an upper end face of a valve body in a sealed manner, the lower ejecting plate is connected with a lower end face of the valve body in a sealed manner, the opening direction of a valve clack is determined, thereby selecting to fetch water from the upper side or from the lower side, if a bidirectional test is needed, testing of one side is performed first, testing of the other side can be directly performed without turning-over of the valve, and thus the efficiency is relatively high.