Using the initial porosity and pore size of precast concrete with EPS particles of different sizes， the axial compressive strength and elastic modulus of concrete with 4 initial porosities and 5 initial pore sizes were systematically studied. The influence law of mechanical properties of concrete with initial defects was analyzed based on the principle of numerical statistics. The results show that the reduction of axial compressive strength and elastic modulus of concrete increases linearly with the increase of initial porosity， and the axial compressive strength reduction increases logarithmically with the increase of initial porosity. Considering the influence of initial porosity and initial pore size， the damage of initial small pore size with initial high porosity is lower than that of initial large pore size with initial low porosity. Compared with the initial pore size， the initial porosity has a more significant effect on the axial compressive strength and elastic modulus of the concrete.