The effects of small dimensions and of quantum dimensions were found in nano-ZrO_2 powder prepared by use of super-alkaline synthetic method at low temperature and quasi-phase change also took place. The nanometer-induced hydration occurred in the process and well growing hydrates was formed when the amounts of the powder mixed with cement were just right. Nano- ZrO_2 powder can improve the microstructure of hydrates, lower the porosity and enhance compressive strength and anti-permeability as consequence of filling action in pores and of bridging action in hardened cement paste.