In the process of asphalt mixture production, aggregates are heated in the drum for a short time at high temperatures, which may lead to cracking due to the heterogeneity of the internal composition of steel slag aggregates. The steel slag aggregates from A, B, and C steel mills were subjected to high-temperature cracking tests under multiple temperature gradients (200 ~ 800 ℃). The cracking conditions of the steel slag aggregates were compared and analyzed. Three factors were discussed: the overflow gas produced by different phases of steel slag at high temperatures, the differences in thermal expansion coefficients, and the internal porosity of the material. The cracking mechanism of steel slag was investigated using XRF, XRD, TGA-FTIR thermogravimetric infrared spectroscopy, SEM microscopic analysis, and a type microscope combined with OpenCV computer vision image analysis. The results show that there are quartzite and Al₃Mg₂ phases in the steel slag, which have higher thermal expansion coefficients than other silicate minerals, making them the main reason for the cracking of the steel slag. The high porosity inside can absorb part of the internal thermal stress, thus inhibiting the cracking of steel slag at high temperatures. Therefore, attention should be paid to the potential risks of steel slag aggregates concerning high-temperature resistance.