Ferrous extraction tailing of nickel slag （FETNS） is the secondary tailings of ferronickel slag （FNS） after ferrous extraction treatment. This paper tests the hydration heat of the FETNS-original portland cement composite binder system using isothermal conductive calorimetry and constructs a hydration kinetics model using the Krstulovic-Dabic model. Both macroscopic and microscopic methods are employed to investigate the basic properties， reaction products， and element leaching of the composite binder system. The results indicate that the hydration kinetics model can accurately reflect the impact of FETNS on the hydration reaction. The incorporation of FETNS reduces the reaction rates and extent of crystal nucleation and growth， phase interface reactions， and diffusion during the hydration process. The addition of FETNS decreases the leaching of reactive elements， delays the setting of the composite binder system， inhibits the formation of hydration reaction products， increases the content of harmful pores in the system’s internal structure， and significantly reduces the early compressive strength.