A pipe joint structure is used to prevent a tube (18) and pipe joint (2), especially fluororesin pipe joint from slipping off. The said pipe joint comprises of a joint body (20), a fixed ring (27) and a union nut (26), being assembled by passing the tube end through said union nut and then though the fixed ring within the union nut. A jig is then used to expand said tube end to become a flared end (180) consisting of a conical surface (181) and a tubular surface (182), and finally connect it to the conical surface and tubular surface on top of the tube connecting portion of said joint body. When said union nut is fastened to the locking thread of said tube connecting portion, its interior recess portion will couple with the bulging surface of fixed ring to ensure it to stay in a concentric position, thereby allowing the tube wall of sealed surface to be compressed evenly and secured firmly on said pipe joint so to achieve a seal and prevent it from slipping off.