Topping-up mechanism and liquid cooling system

The utility model discloses a topping-up mechanism and liquid cooling system, wherein, this topping-up mechanism contains a lower cover, an upper cover, a piston, an at least elastic component and an at least damping piece. The lower cover has a liquid outlet, and cover connection in lower cover. A cavity is between lower cover and upper cover. The cavity is linked together and holds a coolant liquid with the liquid outlet. The upper cover has a shaft hole. The piston is movably to be set up in the cavity. The piston has an axostylus axostyle, and the axostylus axostyle is worn to locate in the shaft hole. The elastic component sets up in the cavity, and the both ends of elastic component difference butt in upper cover and piston. The damping piece sets up on the axostylus axostyle and butt in the inner wall in shaft hole.