In order to promote engineering application of iron tailings, taking Benxi high silicon iron tailings in Liaoning Province as an example, the effects of different mechanical activation methods and time on the activity and morphology of iron tailings were studied. The effect of mechanical activation on the particle size distribution, specific surface area, activity index and pozzolanic activity of iron tailings were detected by grading analysis, mortar test, lime adsorption test and so on. The hydration reaction mechanism of cementitious system was explored by X-ray diffraction and scanning electron microscopy analysis. The results show that mechanical activation can refine the partical size of iron tailings, increase the particle roundness and reduce surface crystallinity. Grinding for 40~60 min has the best effect. The activity index is up to 96.6% after wet grinding for 50 min, and the pozzolanic activity is significantly enhanced. The activation effect of wet grinding is better than that of dry grinding. Mechanical activation promotes the secondary hydration reaction between iron tailings and cement, and improves the performance of cementitious system.