Effects of two types of polyether shrinkage reducing agent(L SRA and S SRA) on hydration process and absolute volume change of fresh cement paste were investigated using helium pycnometer, hydration heat and X ray diffraction（XRD）. The results show that hydration process of cement paste in early age is retarded by the shrinkage reducing agents. Curves of flash shrinkage stage, shrinkage suspension stage, and shrinkage slowdown stage are in good agreement with heat flow. Time of the inflection point during fast shrinkage stage is consistent with the time of heat flow peak. There exists a mutually corresponding relationship between absolute volume change and heat flow, which explains the delay effect of shrinkage reducing agent on hydration of cement paste.