Abstract: 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.