Performance degradation of concretes with varied water cement ratio and air content under freeze thaw cycles or salt frost cycles were investigated. After suffering from salt frost, microstructures of hardened cement pastes were analyzed by mercury intrusion method and scanning electron microscope, and chloride transport performance was measured experimentally. The results show that, mass loss of concrete after 25 times of salt frost cycles is 10 times of that after pure water frost. At early stage of freeze thaw cycles, there is a small descent of dynamic elastic modulus of concrete after salt frost compared with the one after water frost. There is a large amount of air voids with size of more than 50μm in air entrained concrete. Mean space of air void in non air entrained concrete is 2.5 times of that in air entrained concrete. Chloride penetration of concrete is weakened by increasing air content. However, chloride ions concentrate in surface layer of concrete, which may be unfavorable for reinforcement protect against corrosion considering the depth of cover to reinforcement.