A UV sterilizer with a double-chamber structure comprises an inner tube and an outer tube with different size, the inner tube being partly surrounded by the outer tube thereby forming an inner chamber and an outer chamber, the inner chamber is the space encircled by the inner tube and the outer chamber is the annular space encircled by the overlapped portions of the inner tube and the outer tube; a first end portion of the inner tube is located outside the outer chamber and provided with a first water port, a second end portion of the inner tube is located inside the outer chamber and provided with a second water port communicating with the outer chamber; a first end portion of the outer tube is sealingly connected with the outer wall of the inner tube, while a second end portion of the outer tube is sealed; sleeved UV lamps are arranged in the outer chamber or in both the inner chamber and the outer chamber.