Concrete　and　rock　are　typical　porous　mediums　which　have　a　great　influence　on　the　elastic　modulus,　strength　and　other　mechanical　parameters　of　concrete　material.　The　effective　bulk-modulus　of　a　composite　with　hollow　spheres　in　a　matrix　is　determined　by　a　three-phase　sphere　model,　and　the　theoretical　formula　of　an　effective　shear　modulus　is　deduced　and　obtained　by　a　hollow　cylindrical　rod　model　proposed　in　the　paper.　Based　on　the　assumption　of　isotropic　materials,　the　effective　Young＇s　modulus　and　Poisson＇s　ratio　are　derived.　Besides,　the　relationships　between　porosity　and　effective　tensile　strength,　effective　compression　strength　and　effective　shear　strength　are　deduced,　and　the　formulas　of　a　quantitative　relation　are　given.　Furthermore,　the　relation　between　porosity　and　critical　strain　when　the　material　with　pores　reaches　the　effective　strength　is　deduced.　The　results　show　that　the　method　proposed　in　the　paper　can　predict　the　effective　mechanical　properties　of　concrete　greatly,　and　the　formula　is　simple　and　easy　to　use.