The effect of triethanolamine, CaCl2 and complex accelerator on the mechanical properties of steel slag-slag powder is studied. Hydration products of the pastes are investigated by XRD. Compared with triethanolamine and CaCl2, complex accelerator can dramatically affect hydration of steel slag and slag powder. The strength of specimen increases with the content of sodium sulfate in complex accelerator increasing, decreases when the content is more than 1.5%. When the content of sodium sulfate is 1.5%, the 3d strength increases to 7.6MPa, 7d strength increases to 7.9MPa, 28d strength increases to 19.5MPa, the vitreous network structure of steel slag can be destructed more thoroughly, more hydration products can be formed. These hydration products are bonded together and fill the void of paste, the density increase, and lead to higher strength. But when the content of sodium sulfate is more than 1.5%, PH value is changed, formation of AFt, hydration of C3S and C2S in later stage is affected, which result in poor strength. The results show that compared with the calcium hydroxide, gypsum and sodium sulfate can stimulate the activity of steel slag more effective. XRD analysis shows that the amount of hydration products is different when the content of sodium sulfate is different. When the content of sodium sulfate is 0.5%, the main products are consist of C-S-H , Ca(OH)2, C2S, C3S and AFt; When the content of sodium sulfate is 1.5%, the main products are consist of C-S-H and AFt, formation of AFt, hydration of C3S and C2S in later stage result in higher strength of paste