Abstract: Thermal simulation technology and modern material microstructure analysis method are adopted to research the effect of cooling time t_8/5 and t_12/8 on the simulated HAZ(heat-affected zone) microstructure transition in 2205 duplex stainless steel.The results indicate that keeping t_12/8 constant and changing t_8/5, the simulated HAZ microstructure and phase proportion almost keep same.So it is not suitable to this material to use t_8/5 as the parameter to investigate the transition behavior of welding HAZ microstructure.When the cooling time t_8/5 keeps constant and t_12/8 is changed, the simulated HAZ microstructure and phase proportion vary largely.Therefore, t_12/8 is the essential factor to affect HAZ microstructure, and it is more suitable to use t_12/8 as the parameter to investigate the transition behavior of welding HAZ microstructure.The effect of the cooling time t_12/8 on the simulated HAZ microstructure is, when t_12/8 increases, austenite gradually transits to branch-like morphology from band-like distribution and appears at the boundary and inside the grain.On the other hand, the ferrite content decreases with the cooling time t_12/8 increasing.In this case, austenite and ferrite in the simulated HAZ microstructure of 2205 contain more dislocation than the base metal.