In order to investigate the elastic modulus of cement‐based composite material, cylindrical specimens with different volume fractions (10%, 20%, and 30%) of aggregate are cast and tested. The effect of transition interface layer properties on the elastic behavior of cement‐based composite material was studied. The Hashin‐Shtrikman theory for evaluating the elastic modulus of two‐phase (aggregate and matrix) composite material is used as a criterion in the analysis. The Double‐Inclusion Method and Mori‐Tanaka Theory are used to predict the elastic moduli of three‐phase (aggregate, transition interface layer, and matrix) composite materials. A comparison is also made between the theoretical results and experimental data. Test results show that the influence of the transition properties on the overall elastic properties of the composite depends on the volume ratio of the aggregate. For high volume inclusion of aggregate, the composite can be considered as a three‐phase material for predicting the elastic modulus of the composite. However, low volume inclusion of aggregate, a two‐phase approach is appropriate.