Abstract: A three-phase composite sphere model is presented for the prediction of Young ’s modulus of concrete1 At amesoscopic level , concrete was considered as a three-phase composite material with aggregates as dispersed phase , interfacial transition zone ( ITZ) as interphase and cement paste as continuous phase1 Applying the simulation technique of concrete mesostructure , the ITZ volume fraction was obtained for a given aggregate grading1 Simulation results show that Li’s approximate method overestimates the ITZ volume fraction and that the ITZ volume fraction is dependant on the ITZthickness , largest aggregate diameter and aggregate grading to a great extent1 By introducing a three-phase compositesphere model , the analytical solution of Young’s modulus of concrete was given1 By comparing the results of both the analytical solution and laboratory experiment , the validity of the model presented is verified1 It is also demonstrated by numerical results that , for a given aggregate volume fraction , the Young’s modulus of concrete increases with the increase ofthe largest aggregate diameter and ITZ Young’s modulus , but decreases with the increase of the ITZ thickness. The aggregate grading also has a greater influence on the Young’s modulus of concrete1