Abstract: Objective The aim is to obtain welding parameters of Q690CFD what meet process requirements. Methods Through the method of welding thermal simulation test, single-pass HAZ thermal simulation testing of Q690CFD was carried out by Gleeble-3800 thermal simulation testing machine. Microstructure, Vickers hardness, and impact toughness of coarse grain HAZ, fine grain HAZ, and inter-critical HAZ under specific heat input were studied. Results The results showed that microstructure types of coarse grain HAZ of Q690CFD under different simulated heat input mainly included bainite ferrite, granular bainite, and M-A component which distributed along grain boundary. With the increase of heat input, impact fracture mode of coarse grain HAZ changed from ductile fracture to cleavage fracture. When heat input was 20 kJ/cm and 25 kJ/cm, although hardness of incomplete phase transition HAZ was slightly lower than that of base material, coarse grain HAZ and fine grain HAZ still had good mechanical properties. Conclusion 25 kJ/cm was selected as actual heat input for Q690CFD welding while meeting the requirements of joint performance and welding efficiency.