Abstract: The Gleeble-3800 thermal simulator was used to simulate the welding HAZ of TSZ410 high-strength economical stainless steel with 5mm thickness. The microstructure of the thermal simulated sample was observed by optical microscope,and the grain size and ferrite ratio were measured. The fracture toughness test was carried out for the thermal simulated samples, and the fracture and crack propagation path were observed by SEM and optical microscope. The results show that the welding HAZ structure of TSZ410 high strength economical stainless steel is composed of martensite and residual high temperature ferrite. With the increase of heat input, the grain size and the ferrite ratio both increase, and the CTOD value decreases. The dimple morphology at crack tip is observed at the fracture with high CTOD value. The effect of grain size on CTOD value is more significant. Finally, it is suggested to increase the formation temperature of high temperature ferrite in steel to obtain more martensite structure in HAZ, so that the toughness of the steel can be improved by tempering.