Abstract: The microstructure and mechanical properties of heat-affected zone (HAZ)of high nitrogen steel (HNS)were investigated by using thermo-simulation technique.The experimental results indicate that the microstructure in the HAZ of HNS is austenite and δ-ferrite under laser welding conditions.The hardness of the coarsegrained heat-affected zone (CGHAZ) increases when the cooling rate increases, and the one of the HAZ decreases while the peak temperature decreases.The results show that the hardness of the HAZ is higher than the one of the base metal, indicating no softening of the HAZ under appropriate welding conditions.The impact toughness of CGHAZ is improved with the increase of the cooling rate, whereas two brickle zones exist in the HAZ.