The work aims to improve mechanical and interfacial transition zone (ITZ) properties of silica fume-doped cementitious materials by reducing agglomeration and aggregation of silica fume particles and enhancing dispersibility. The surface of silica fume was modified in the methods of chemistry graft reaction and mechanical dispersion. Then surface potential, superplasticizer adsorption capacity and particle size distribution, and microstructure of the silica fume particles and hardened silica fume-based cement paste were characterized in such test methods as surface potential measurement, ultraviolet spectrum analysis, laser particle size analysis and scanning electron microscope. Prism specimens were employed to evaluate the effects of modified silica fume on flexural strength and compressive strength of cement-silica fume paste. After the surface was modified with aminopropyltriethoxysilane and magnetic stirring process, surface potential of silica fume changed from ?21 mV to +3 mV, adsorption capacity to high performance polycarboxylate-based superplasticizer increased by 60%. Quantity of nano-scale fine particles in the silica fume increased significantly, agglomeration to large particles decreased obviously, and dispersibility of silica fume particles improved greatly. Mechanical properties of cement-silica fume paste were improved by 11%~24% due to the modified silica fume. After surface modification is applied to original silica fume using amino siloxane and magnetic stirring process, surface potential of silica fume is changed from negative to positive, superplasticizer adsorption capacity is increased significantly, agglomeration of particles is reduced, quantity of nano-scale particles is increased, and dispersibility in cement is improved, ITZ performance of cement-silica fume hydration products is improved, and mechanical properties of cement-silica fume paste is greatly improved.