To calculate the volume fraction of interfacial transition zone(ITZ) in cement-based composite materials,two quantitative expressions combining with actual sieve curve were put forward based on the most nearest surface distribution function and an approximate way of surface area of aggregates.The results show that the error of the ITZ fraction was about 10 percent,when the volume fraction of aggregate and the ITZ thickness per unit volume concrete is less than 0.5,50 μm,respectively,and the smaller the ITZ thickness,the smaller the calculated difference between two methods.