The utility model discloses a tail gas waste heat recovery device of a gas engine, and belongs to the technical field of oil field auxiliary processes. The device comprises an inner sealing cylinder (14), an outer sealing cylinder (15), a first pressure end socket (13) and a second pressure end socket (12), the inner sealing cylinder (14) is arranged in the outer sealing cylinder (15); the two ends of the inner sealing cylinder (14) extend to form the first pressure end sockets (13), and the two ends of the outer sealing cylinder (15) extend to form the second pressure end sockets (12). The first pressure seal head (13) and the second pressure seal head (12) are convex seal heads; and a water tank chamber (3) is defined by the inner sealing cylinder (14), the outer sealing cylinder (15), the first pressure seal head (13) and the second pressure seal head (12). By using the device, perforation leakage of a weld joint of the water tank chamber can be reduced, and meanwhile, exhausted tail gas is effectively silenced and cooled.