To promote the extensive application of steel slag in cementitious materials, it is the key that the hydration activity of steel slag is improved. The early hydration process and properties, and hydration kinetics of steel slag cement with different sodium salts were investigated by hydration heat measurement, scanning electron microscopy (SEM) and hydration kinetics simulation. The results showed that the hydration process of steel slag-cement was not changed by the addition of sodium salt. The hydration process could be divided into rapid exothermic, induction, acceleration,deceleration,and decay stages. The hydration is controlled by nucleation and autocatalytic reaction in the acceleration stage(N＜1)and by diffusion in the decay stage(N > 2), while in the deceleration stage (1 < N < 2), the hydration is controlled by both chemical reaction and diffusion. Due to different kinetics and mechanism of hydration vary in different stage, the reaction rate constant in the acceleration stage is 6~8 times that in the attenuation stage. The reaction rate constant (K) of steel slag-cement added sodium salt is larger than not added sodium salt,and its hydration reaction is accelerated.