Compressive　stress　and　tensile　stress　were　applied　to　concrete　specimens　using　test　rigs　designed　by　RILEM　TC　246-TDC.　Ultrasonic　wave　velocity　and　autoclam　permeability　system　were　used　to　characterize　the　damage　variable　and　gas　permeability　coefficient　of　concrete,　respectively.　The　experimental　results　show　that　the　strain　value　of　concrete　increases　with　the　increasing　of　stress　level　and　loading　time.　The　damage　variable　and　gas　permeability　coefficient　of　concrete　under　compressive　stress　decrease　at　first　and　increase　after　a　threshold　value　between　0　and　0.6.　When　the　concrete　is　under　tensile　load,　the　damage　variable　and　gas　permeability　coefficient　increase　with　tensile　stress,　with　a　significant　increase　from　0.3　to　0.6　tensile　stress.　There　is　a　strong　linear　relationship　between　the　damage　variable　and　the　gas　permeability　coefficient,　suggesting　both　as　good　indicators　to　characterize　the　damage　of　concrete　under　stress.