Abstract: The hardened cement paste in waste concrete is the part of the largest energy and resource consumption, the worst environmental impact and the most economic costs. The preparation of silicate dehydration phase and characterization are studied. The results show that a material called silicate dehydration phase can be obtained from the hardened cement paste after calcination, and rehydration hardening structure is obtained by adding silicate dehydration phase substance and water. The biggest rehydration strength of hardened cement paste dehydration phase is derived at 650℃. The research on performance of silicate dehydration phase-silica powder is studied. In order to improve the strength of dehydration phase, the modification for adding silica powder is carried out, the strength is improved after adding microsilica powder.