<p>In this work, a simple processing method that involves adding aluminum was adopted to improve the properties and structure of 7CrSiMnMoV die steel. The comprehensive mechanical properties are tested, and the microstructure and fracture morphology are analyzed by an optical microscope and a scanning electron microscope-energy dispersive spectrometer. The enhanced mechanisms are analyzed by investigating typical inclusion characteristics and in-situ observation of re-crystallization and solidification behavior. Results show that the tensile strength of the cast ingot steel increased from 722.55 MPa to 1025.30 MPa as the aluminum concentration increased from 0.026% to 0.54%. Meanwhile, it inherits superiority after quenching and tempering; the strength increased from 1070.35 MPa to 1191.94 MPa. It mainly contributes to the modification of the network eutectic cementite and the formation of the Mn(Ca)S-wrapped MgAl₂O₄ complex inclusions by adding aluminum. In-situ observation found that it can inhibit re-crystallization behavior and reduce the eutectic reaction temperature range from 1287°C to 1271°C, shifting to 1308°C to 1275°C with aluminum concentrations increasing from 0.026% to 0.54%, which is unfavorable for forming network eutectic cementite.</p>