Abstract: In order to realize the recycling utilization of Pisha sandstone, Pisha sandstone was transformed to modified steel slag/Pisha sandstone composites which had good mechanical properties by alkali-activated method and mixing with suitable amount of steel slag. Then, the effects of dosages of steel slag, alkali-activator and age on compressive strength and softening coefficients of modified steel slag/Pisha sandstone composites were investigated systematacially. Finally, SEM/EDS, FTIR and XRD were used to analyze the hydration process and carbonation process of modified steel slag/Pisha sandstone composites. The results show that the 90 d compressive strength and softening coefficient of modified steel slag/Pisha sandstone composites achieve 46.0 MPa and 0.94 respectively, which fully meet the requirements of engineering application. The main hydration products of modified steel slag/Pisha sandstone composites are C-S-H gel and geopolymer gel, and C-S-H gel has relatively serious carbonation phenomena. When the dosages of steel slag and NaOH are 20.0wt% and 1.5wt% respectively, the 28 d carbonation rate of C-S-H gel reaches 30.1%, and carbonation rate decreases with the dosages of steel slag and NaOH increasing, but carbonation rate has little effect on strength. Modified steel slag/Pisha sandstone composites have good mechanical properties and water resistance.