The invention discloses a flanging die and belongs to the field of pipeline machining tools. The flanging die comprises a shell, a straightening sleeve, a shaft body and a shaft sleeve; the straightening sleeve is fixedly installed in the shell; the shaft sleeve comprises a first installing part and a first machining part; the first installing part is located in the shell and is fixedly connectedwith one end of the straightening sleeve; the shaft body is movably and coaxially inserted in the shaft sleeve, and comprises a second installing part and a second machining part; the second installing part is sleeved with an elastic piece; the elastic piece is arranged between a clamping table and the second machining part; the second machining part comprises a first cylinder, a second cylinder and an inclined table; the second cylinder is arranged in the first machining part; the end portion of the first cylinder stretches out of the first machining part; the diameter of the first cylinder is smaller than that of the second cylinder; the inner wall of the first machining part and the peripheral wall of the second cylinder are in sliding fit to form a machining groove matched with a screwthread chamfer of a to-be-machined pipeline. The flanging die solves the problem that the operating procedure of flanging is tedious.