Abstract: In order to solve the problems of shrinkage and creep in concrete, a research of mechanism and impact factors of chemical shrinkage, autogenous shrinkage and drying shrinkage in PC-CSA composite cement, was conducted in this paper. SEM and MIP were used to perform the properties of Portland cement and calcium sulfoaluminate composite cements.The relationship between shrinkage of microstructure and strength, and the effects of cement phase content were discussed though a comparative study between OPC and PC-CSA composite cement. Results show that chemical shrinkage can be changed directly by adding expansive components. The effects of autogenous shrinkage are bigger than that of drying shrinkage. There is a new method to testing porosity by SEM. The critical range of the best yield of unhydrated cement mineral is 30%-45% obtained fromcomparing the results of MIP. The pore structure is changed and micro-expansion appears by adding expansive components at hydration one day. It is consistent with the actual measurement results of cement volume changes.