In order to solve the problem of chloride erosion in reinforced concrete, the effects of different dosages of ground granulated blast furance slag(GGBS) on working performance, mechanical properties and chloride binding capacity of cement paste were studied, and the chloride binding mechanism was characterized and analyzed by phase composition, thermogravimetric analysis, pore structure distribution and thermodynamic simulation. The results show that the GGBS can improve the working performance of cement-based materials, and effectively improve the compressive strength and chloride binding capacity of cement paste at the later stage. The comprehensive performance is the best when the GGBS content is 30% (mass fraction). The GGBS can chemically combine with chloride ions to promote the formation of Friedel’s salt and Kuzel’s salt, and the pozzolanic effect can increase the content of C-S-H and refine the pore structure of hardened slurry to improve the compactness. The chloride binding capacity of the cement paste with GGBS is affected by the chemical binding, physical adsorption and migration resistance of chloride ions. With the increase of the content of GGBS, the chloride chemical binding and physical adsorption ability of the cement paste gradually increase, and there is an optimal content of GGBS for migration resistance. This study provides technical and theoretical support for using GGBS cement based materials in offshore islands.