The eff ects of tempering temperatures on the microstructure and mechanical properties of the simulated coarse-grain heataff ected zone (CGHAZ) and inter-critical heat-aff ected zone (ICHAZ) were investigated for a high-strength–high-toughness combination marine engineering steel. The results demonstrate that the microstructure of the simulated CGHAZ and ICHAZ after tempering is characterized by tempering sorbites and coarse grain in the simulated CGHAZ. As tempering temperature increases, the tensile strength of the simulated CGHAZ and ICHAZ decreases and the Charpy absorbed energy of the simulated ICHAZ at − 50 °C increases remarkably, but the impact toughness of the simulated CGHAZ is not improved. After tempering at 550 °C, the coarse fl ake carbides, which distribute at the prior austenite grain and martensite lath boundaries, deteriorate the impact toughness of the simulated CGHAZ. With the increase in tempering temperature, the morphology and the size of the carbides gradually change from coarse fl ake to fi ne granular, which is benefi cial to the improvement of impact toughness. However, the coarse-grain size of the simulated CGHAZ and the M 23 C 6 -type carbide precipitated along the grain boundaries weakens the enhancing eff ect of carbides on impact toughness.