Abstract: Thermodynamic equilibrium phase diagram of low carbon steel with different carbon content and combined addition of aluminum and boron was calculated through the Thermo-Calc thermodynamic software. The solid solution and precipitation behaviors of carbon, aluminum, and boron elements in the low carbon steel, as well as the microstructure, mechanical properties and anti-aging properties of the test steel, were studied. The results show that the content of dissolved free carbon atom in the test steel matrix increased with the carbon mass fraction from 0.003% to 0.020%. When the carbon mass fraction increased to 0.053%, the precipitation of cementite in the steel increased and the dissolved free carbon atom decreased. After the combined addition of aluminum and boron in the low carbon steel, the nitrogen atom precipitated in the form of AlN and BN, resulting in the decrease of the dissolved free nitrogen atom. The carbon content and combined addition of aluminum and boron had little effect on the tensile properties of the test steel at room temperature. With increasing carbon content, the grain size of the test steel decreased gradually, and the aging index increased first and then decreased. The test steel showed the worst aging resistance at the carbon mass fraction of 0.020%, and the combined addition of boron and aluminum could improve its aging resistance.