The utility model relates to a quenching boiler which is characterized in that the utility mode is mainly composed of an inlet end cover (1), a lower connecting flange (2), an inlet tube plate (3), a lower connecting piece (4), a barrel body (5), an upper connecting piece (6), an outlet tube plate (7), an upper connecting flange (8), an outlet end cover (9), and a heat exchange tube (10) from bottom to top in sequence. The inlet tube plate (3) and the outlet tube plate (7) are both thin tube plates. The lower connecting piece (4) and the upper connecting piece (6) are both reducer tubes. The connecting pieces can perfectly absorb thermal stress through a half expansion joint shape. The welded joints of shell side spaces are all butt welding joints, the welding between the heat exchange tube and the tube plate is formed to realize butt welding through deep hole welding. The reverse side of the inlet tube plate adopts a heat resistant alloy overlay welding layer, and has perfect thermal protection function to the inlet tube plate. The quenching boiler of the utility model has the advantages that the structure is simple, simultaneously, the material consumption is small, the overall fabrication cost is low, and the quenching boiler not only can be used for the building of a new ethylene cracking device, but also can be suitable for the modification of an ethylene cracking device in service.