Pore pressure and thermal dehydration of concrete are two major factors which affect the spalling of concrete at high temperatures. Thermal dehydration can cause deterioration of concrete properties and promote the development of micro cracks in the skeleton of concrete. Pore pressure will also be influenced by dehydration when the hydrated water enters the micro pores. In the current study, a framework of elastoplastic damage constitutive model is developed to described the mechanical behaviour of concrete and pore pressure at high temperatures. Both load induced damage and thermal dehydrated damage are considered. The thermal dehydrated damage is temperature related, which reflects the impact of temperature on concrete properties. A model of pore pressure is developed by considering the influence of thermal dehydration and damage related permeability. The pore pressure field associated with vapor, liquid water and dry air is predicted and compared with experimental results.