The microstructures and impact toughness of thermal simulated welding HAZ in 2205 duplex stainless steel were studied by means of thermal simulator and impact testing in the paper. The influences of cooling time on the impact toughness of thermal simulated HAZ were investigated also. The results show that the cooling time has strong effects on the impact toughness of the thermal simulated HAZ, that the ferrite content and micro hardness decreases as increasing of cooling time, that the microhardness in ferrite is lower than that than in austenite, that impact toughness increases with the increase of the cooling time t12/8 for a certain cooling time t8/5, and that impact toughness decreases with the increase of the cooling time t8/5 for a certain cooling time t12/8.