Steel slag is a green and recyclable cementitious material with limited application value due to its low activity. This paper aims to investigate the effects and mechanisms of different activation methods on the activity of steel slag,and to experimentally verify the effectiveness of three methods: alkaline activation, acid modification + alkaline activation, and ultrasonic cavitation + alkaline activation. This study also explores the effects of acid modification and ultrasonic cavitation on the strength development of steel slag. The results showed that acid modification mainly improves the early strength,but the generation of calcium formate consumes Ca(OH)₂ and reduces the alkalinity of the environment,resulting in weaker later strength. In contrast, ultrasonic cavitation can remove the inert components on the surface of steel slag,promote the dissolution and reaction of active substances such as C₂S and C₃S, and accelerate the hydration reaction and formation of C—S—H gelling material,thereby improving the strength of the cementitious system.The methods and results presented in this paper can provide new ideas and directions for the treatment and utilization of steel slag.