Cement-based material can be regarded as a highly heterogeneous material with multiple scales and the elastic constants have different values at different scales. To obtain a global elastic constant for a cement-based composite, a homogeneous method is used to perform the upscaling process. This paper presents a method to obtain the global elastic modulus for cement paste with consideration of capillary water pressure. The elastic modulus of different phases is determined using nano-indentation tests. The volume fractions of different phases in the cement paste are determined by using an isothermal conductive calorimeter and a cement hydration kinetic law at early age. The global elastic modulus of cement paste is calculated based on a self-consistent scheme. Considering that, at very early hydration of cement paste with a high water-to-cement ratio, water occupies a relatively high fraction and its pressure may influence the elastic properties of the paste, capillary water with capillary pressure is considered instead of pure air voids without mechanical properties during the upscaling process in this investigation. The global elastic modulus obtained in this way is compared with the value obtained from impact experiments and good agreement is found. © 2012 Thomas Telford Ltd.