Water absorbing and releasing property of lightweight aggregate (LWA) in concrete and its influence on microstructure of interfacial zone as well as frost-resistance of combined aggregate prepared with different water absorption LWA and w/b ratios were investigated. The results show that, as for concrete with low w/b ratio, the 28d frost-resistance of concrete prepared with high water absorption LWA is worse, however with the increase of curing age, the 90d frost-resistance of concrete improves obviously, which is due to the water releasing of LWA that leads to the recovery of its air entraining effect as well as the densification and thicken of interfacial zone. So the LWA with moderate water absorption should be selected to prepare the low w/b ratio concrete. As for concrete with high w/b ratio, the frost-resistance of concrete prepared with low water absorption LWA is the best. This is account for the dense shell of ceramsite that could reduce the soakage from loose cement paste under frozen pressure.