The　micro　defect,　namely　the　micro　cracks　and　different　kinds　of　pores　randomly　distributed　within　concrete,　affects　the　failure　mechanism　and　macro-mechanical　performance　of　concrete.　Because　concrete　porosity　changes　with　the　variation　of　external　load,　porous　concrete　is　simplified　to　be　a　hollow　sphere　model　in　this　study.　On　the　basis　of　the　theory　of　elasticity,　the　quantitative　relationship　between　current　porosity　of　concrete　and　initial　porosity　as　well　as　concrete　body　strain　is　deduced.　The　effective　elastic　modulus,　effective　Poisson＇s　ratio　and　the　peak　strain　of　concrete　with　micro-defects　are　obtained.　A　piece-wise　linear　equivalent　constitutive　relation　model　of　concrete　for　uniaxial　loading　cases　is　drawn.　Finally,　by　using　the　meso-element　equivalent　method,　the　macro-mechanical　performances　of　concrete　with　different　porosity　under　uniaxial　loading　are　investigated.　The　influence　of　porosity　variation　on　the　deformation　of　concrete　is　discussed.