The volume expansion and separating water of submicron cement after solidification can not be explained by existing theories. In order to explore its mechanism，G-grade，ultra-fine and submicron cement slurry were cured at high temperature of 95℃ under sealed condition. Their deformation during hydration process had many similarities and obvious differences. It was concluded that in different hydration stages，the particles of hydration products in the slurry experienced the mutual exclusion， mutual pulling and mutual extrusion，which was the fundamental reason for the micro expansion，shrinkage，cracking，expansion， separating water and many other phenomena of the slurry in turn. On this basis，referring to the research results of other scholars，acement slurry hydration deformation model was constructed，which could provide a reasonable explanation for some phenomena.