In this paper, experimental studies of a new kind of cementitious materials by using sludge and rice hush ash as the raw materials and sodium silicate as activator are introduced. The effects of the rice hush ash, lime content, sodium silicate dosage and curing age upon the mechanical properties and water resistence of the cementitious materials are analysed, and the scanning electron microscope (SEM) is used to observe the microstructure of the new cementitious materials. The experiment results show that the mechanical strength and water resistence of the cementitious materials are impacted notably by the curing age, rice hush ash, lime content and sodium silicate dosages, and that the influence factors in order of importance are rice hush ash dosage, sodium silicate dosage and lime dosage. The maximum compressive strength of the specimen was up to 15.30 MPa and the corresponding softening coefficient was 0.93 at 56 days. The observed results of the scanning electron microscope (SEM) show that the flocculent reaction products based on silt-rice husk ash cementitious materials are mainly uniform dense floccule gel (hydrated calcium silicate gel C-S-H) and a small amount of the block crystal CaCO3.