The long term water absorption of aggregates including artificial basalt, diorite, limestone and natural granite as well as its influence on deformation of MgO concrete were investigated. The cracking sensitivity of MgO concrete made from different aggregates was measured by advanced temperature and stress equipment (TST machine). Results indicated that obvious increment in water absorption of aggregates from 24h to 180d was observed and self shrinkage and drying shrinkage of concrete was closely related to water absorption of aggregates. The higher the water absorption, the bigger the shrinkage of concrete. Lower cracking temperature of MgO concrete made from basalt and diorite was shown according to the results of TST machine test.It is also shown that enrichment of Ca and Mg on interfacial transition zone of these two concretes was more obvious which implied denser compaction of hydration products favoring crack resistance of concrete.