In order to promote the application of steel slag in road engineering and alleviate the problems of land occupation and environmental pollution caused by steel slag stockpiling, the physicochemical characteristics of steel slag during aging and the performance of steel slag asphalt mixtures were investigated. The morphological characteristics and mineral composition of steel slag before and after aging were investigated using particle size and shape and XRF(X-ray fluorescence spectroscopy) tests. Subsequently, asphalt mixtures were prepared using untreated steel slag, aged steel slag and basalt, and the volumetric expansion, water stability, high-temperature stability and low-temperature cracking resistance of the three asphalt mixtures were comparatively evaluated. In addition, the correlation between aggregate properties and mix performance was analysed by grey correlation method. The results show that the high roughness and angularity of steel slag make it an ideal substitute for natural aggregates such as basalt. However, the poor volume stability of unaged steel slag and its tendency to swell in contact with water resulted in its inability to meet the requirements for pavement use. It is worth noting that CaO and Fe₂O₃ contents are important factors affecting the volumetric stability of steel slag, and aging treatment can reduce these negative effects to a certain extent, thus improving the road performance of steel slag asphalt mixtures. Comprehensive analyses, aged steel slag asphalt mixture has better comprehensive road performance, and the secondary use of steel slag is of great significance to achieve sustainable development of road infrastructure.