The invention discloses a U-shaped pipe non-return device which comprises a first pipe segment, a second pipe segment and a third pipe segment; the first pipe segment and the second pipe segment are perpendicular to the plane and arranged in parallel, and the third pipe segment is longer than the first pipe segment. One end of the first pipe segment is connected with a main water supply pipe, and the other end of the first pipe segment is connected with one end of the second pipe segment; one end of the third pipe segment is connected with the other end of the second pipe segment, the other end of the third pipe segment is connected with a C3 condenser through a second water supply branch pipe, and side cold water is prevented from flowing back to the C3 condenser from a C2 condenser. According to the U-shaped pipe non-return device, the dual functions water supply and vacuum backflow prevention are achieved through a U-shaped pipe with pipes on the two sides having a height difference are achieved, work is more reliable, a mechanical clamping fault is avoided, influences of impurities in water are avoided, water supply resistance is small, sealed vacuum is tight, and zero leakage can be achieved.