Abstract: In this paper, by weld thermo-simulation test with different peak temperatures, the variation of HAZ charpy impact toughness of Cr-Al steel was determined. The results obtained from the test showed that when the peak temperature of single thermal cycle increased,the HAZ impact toughness decreased, the fractographic appearances changed from dimple pattern to cleavage or quasicleavage one, the grain size of prior austenite grew, and the martensitic laths became wide. It was also found that the excellent properties of welding joint could be obtained by applying multiple thermal cycle. By increasing the peak temperatures the HAZ impact toughness could be increased, and the fractographic appearances could be changed from brittle characteristic to ductile one.