A numerical model is proposed to simulate the exothermic hydration process of cement and temperature rise in mass concrete pours. The hydration reaction of each major mineral compound found in Portland cement, C3S, C2S, C3A and C4AF, is considered. The hydration of each mineral compound is characterised by its two material functions, namely, the thermal activity and the reference rate of heat of hydration. The influences of various factors on the exothermic hydration process are taken into consideration. The applicability of the proposed model is verified by a series of adiabatic temperature rise tests. With the establishment of this approach, it is possible to simulate the exothermic hydration process of Portland cement and the temperature rise directly on the basis of intrinsic mechanism of hydration, chemical composition of cement and mix proportion of concrete mixture.