Abstract: The heat treatment of 0.20 wt%-0.65 wt% C steel was carried out by CS-1V hexahedral top high-pressure equipment under 2 GPa high pressure. The effects of high-pressure quenching on the microstructure and mechanical properties of martensite in carbon steel with different carbon contents were studied by SEM and EBSD. The results show that the hardness of carbon steel after heat treatment under 2 GPa high pressure is obviously higher than that of normal pressure quenching, and the hardness change is not obvious when the carbon content is less than 0.45%. When the carbon content reaches 0.45%, the proportion of twin boundaries increases and the hardness increases obviously. When the carbon content reaches 0.65%, the hardness decreases slightly.