Abstract: The hydrous reaction processes of each component of clay hardening grouts (CHG) and catalytic mechanics of the hardening agent in the CHG have been studied and analyzed in the paper. The microstructure of the reaction products and intermediate products in hardening process of CHG are studied with scanning electron microscopy (SEM). The catalytic mechanics of hardening agent has been proved. On the basis of the analysis and study, the hardening model of clay hardening grouts is proposed.