Abstract: The micro porosity, existing in a random distribution of location and volume, makes great effect on the microstructure and mechanical properties of materials. In the study, the effect of micro porosities on the microstructure of compacted graphite cast iron was analyzed by micro-structural observation. At the same time, the representative volume element model representing the micro porosity was built up. Then, applying the periodic boundary conditions and tensile displacement load, the effects of micro porosity on mechanical properties of compacted graphite cast iron were investigated. The results show that Ce and Mg elements exist in the border of micro porosities, which indicates that these elements have a close relation with the micro porosity formation. Besides, the numerical analysis indicates that equivalent Young's modulus decreases linearly with the volume fraction of micro porosity increases. Moreover, stress concentration is found to be obvious in the vicinity of micro porosities, which can prompt the initiation and propagation of micro-cracks.