Hydration mechanism and performance of tri-cementitious material, which contains clinker, limestone powder and fly ash, are studied. It is showed that when mixed materials ratio increases from 20% to 40%, the water amount for standard consistency will increase remarkably, and when dosage of limestone powder is 50% in mixed material, the water amount for standard consistency will reach minimum, i.e. 26%; but when limestone powder ratio reaches 40%, the fluidity of slurry reaches maximum, and then it drops with increasing of limestone powder ratio. It is also found that increasing of dosages of mixed materials will decrease flexural strength and compressive strength, and increasing of ratio of limestone powders can result in decreasing of compressive strength at 28 days curing time, especially when ratio of mixed material is 20%. In order to explain the rules that above-mentioned, the particles size distribution is studied, and the hydration mechanism is analyzed.