Properties of reactive powder concrete (RPC), such as strength, dynamics elastic modulus, air permeability, carbonization, and dilation potential under long-term heat treatment condition were investigated. The pore structure and microstructure of RPC were also studied by mercury intrusion porosity and scanning electron microscope. Furthermore, relationships between properties and microstructure were analyzed and an ideal mecrostructure of RPC was put forward. Results indicate that RPC possesses very low porosity and its air permeability is lower by 1—2 magnitudes than that of conventional concrete. No expansion in length was observed for samples subjected by heat treatment at 90 ℃ water for 21 d. The excellent properties of RPC benefit from its dense and homogenous microstructure.