A volume measurement system and method for a closed water-filled karst cave, including a water collecting device, concentration tester and control system. The control system is connected to the water collecting device by a connecting piece. The water collecting device is a container with a top closed and bottom open. The water collecting device top is a piston. The piston is connected to a propulsion rod, and propulsion rod is controlled by control system to extend or retract, so as to realize the forward or backward movement of the piston. An openable and closeable placement table is hinged to the water collecting device's inner wall. The placement table is connected to piston, the placement table moves upward when piston is raised, and placement table moves downward when piston is lowered. The placement table is configured to accommodate a chemical substance. The concentration tester is configured to detect the solution's concentration.