Abstract: By virtue of the nearest surface function formula , this cont ribution gives a quantitative formula to calculate the volume f raction of interface in concrete. A random point sampling approach was used to verify the feasibilityof the aforementioned formula. In addition , for the concrete in which the aggregate follows the Fuller dist ributionfunction , this formula was employed to elucidate the variation of the ITZ volume f raction with the aggregate volumef raction at various ITZ thicknesses. The analytical formulas were further derived to illuminate the different effect son volume f raction of ITZ among ITZ thickness , volume f raction of aggregate , and particle size dist ribution of aggregate. Both qualitative and quantitative approaches were put forward to evaluate the overlapping degree betweenneighboring ITZs. The result s indicate that for the concrete with common-used range of aggregate volume f raction ,the influencing order of these three factors on the ITZ volume f raction as well as on the overlapping degree of neighboring ITZs is : ITZ thickness > volume f raction of aggregate > fineness of aggregate.