Abstract: The thermal cycling curves of the HAZ were measured by infrared thermal imager under different heat input conditions for super austenitic stainless steel 254SMo. The effects of peak temperature and cooling time on the microstructure and mechanical properties of heat affected zone were studied. The results show that the austenite grains grow in the heat affected zone with the increase of the heat input. When the heat input increase up to 1.61 kJ /mm, the average size of the austenite grains increases from 9.12 μm to 16.37 μm, and meanwhile the precipitation of the χ phase occurs. The microhardness and impact properties of welded joints were investigated. The results indicate that the welded joint has excellent integrated mechanical properties at the heat input of 1.46 kJ /mm.