The application of steel slag to pavement subgrade can improve the comprehensive utilization of steel slag as well as help to reduce the consumption of natural sand and gravel materials. In order to analyse the effect of steel slag fine aggregate on road performance of cement stabilised sandstone base layer (CSSB), the compressive strength, splitting strength, shrinkage properties and water stability of CSSB were comparatively analysed under different steel slag fine aggregate replacement limestone fine aggregate, and SEM combined with energy spectroscopy were used to reveal the effect of steel slag fine aggregate on microstructure of CSSB. The results show that steel slag fine aggregate can effectively improve late strength of CSSB, in which the 60 d strength of CSSB with 100% steel slag fine aggregate replacement rate increases by 18.7% compared with that of undoped steel slag specimens, however, there is a certain negative effect on the early strength of CSSB. Steel slag fine aggregate can improve shrinkage properties of CSSB, and the higher the doping amount, the more obvious the improvement of the performance. Although steel slag fine aggregate can improve the long-term water stability of CSSB, it will reduce its short-term water stability to some extent. Compared with the undoped steel slag samples, m(Ca)/m(Si) ratio in the interface transition zone of CSSB with 100% steel slag fine aggregate replacement rate at the age of 28 d reduces by 62.95%, and the C-S-H gel is obviously increases, with a denser structure. The study shows that by controlling the reasonable content, steel slag fine aggregate can be used as a substitute aggregate for traditional sand and gravel fine aggregate, and has a good application prospect in the pavement base layer.