A high-pressure pump includes a pump cover, an air cylinder, a piston, a water cooling device, and a pump seat. The air cylinder is formed by a first air cylinder, a second air cylinder and a third air cylinder whose diameters are progressively reduced and that are coaxially disposed. The piston is also formed by a first piston, a second piston and a third piston whose diameters are progressively reduced and that are respectively disposed in the first air cylinder, the second air cylinder and the third air cylinder. A water cooling device is disposed between the second air cylinder and the third air cylinder.