Abstract: To obtain reasonable welding heat input and accurately predict heat affected zone width of 12Cr1 MoV heat-resistant steel pipe for controlling boiler welding quality, the thermal circling curves of typical position on steel pipe was obtained by numerical simulation with ANSYS software based on different welding process parameters. Compared the simulation results and the experimental results, it was found that the values calculated of thermal circling curves were close to the ones measured by infrared thermometer. Moverover, the simulation width of welding heat-affected zone was basically the same as the measured value.Welded joint microstructure is mainly acicular ferrite, and heat affected zone microstructure is mainly proeutectoid ferrite and quasi-eutectoid sorbite, while overheated zone have a small amount of ferrite and granular bainite.