Steel slag shows excellent carbonization properties, due to the high alkalinity. However, the stability of steel slag has restrict its large-scale utilization in building materials. The accelerated carbonation treatment of steel slag is expected to solve the problem of stability, and then make it safely used for building materials by achieving coordinated consumption of solid waste and carbon dioxide. In this study, the influence of pretreatment (hot splashing and pressure-hot stew) on the carbonization performance of steel slag sand were systematically studied. The results shown that carbonization can lead to the reduction of autoclave chalked ratio and apparent density of steel slag sand, with improving fineness. The CO2 uptake rate of the pressure-hot stewed steel slag sand is generally higher than that of the hot splashed steel slag sand under the same carbonation time, and the maximum CO2 uptake rate of steel slag sand is 3%. Since the index of autoclave chalked ratio alone is not reliable to determine the stability of steel slag sand as aggregate, the autoclave stability index should also be considered. The autoclave stability of carbonated steel slag sand is closely related to the pretreatment of steel slag. The pressure-hot stewing steel slag sand shows better autoclave stability after carbonation. The finding can provide the possibility and theoretical basis for the application of carbonized steel slag as fine aggregate.