The invention discloses a body of waste heat boiler, comprising a transition section flue which comprises an ascending part and a descending part, wherein, the top end of the ascending part is connected with the top end of the descending part, and a convection section flue, wherein, a smoke inlet of the convection flue is connected with the lower end of the descending part of the transition section flue and a smoke outlet forms at the smoke discharging end of the convection section flue. According to the boiler body of the invention, since the transition section flue is arranged, high temperature flue gas containing dust enters into the ascending part of the transition section flue from a melting furnace and the dust contained in the high temperature flue gas can fall by depending on gravity during ascending process, thus the dust is not easy to stick on inner wall of the boiler body and accumulated dust is light in the boiler body, thus reducing dust removal operation, improving service life of the boiler body, prolonging operation time of the high temperature flue gas in the boiler body and improving recycling efficiency of the waste heat.