The constant temperature and pressure molecular dynamics (MD) have been performed to investigate the isothermal bulk modulus of MgO under high pressures and temperatures, using the shell model (SM) potential functions consisted of the Coulomb, dispersion, and repulsion interactions. In order to take account of non-central forces in crystals, the breathing shell model (BSM) is also introduced in MD simulation, in which the repulsive radii of oxygen ions are allowed to deform isotropically under the effects of other ions in the crystal, with each core and breathing shell being linked by a harmonic spring with force constant k. The isothermal bulk modulus K-T of MgO dependence of the compression ratio VIVO and the pressure P have been obtained from MD runs at T=300 and 2000 K, and compared with the available theoretical results. Compared with SM potential of Stoneham and Sangster [Phil. Mag. B 52 (1985) 717], the MD results with potential of Lewis and Catlow (LC) [J. Phys. C 18 (1985) 1149] are found to be in good agreement with the studies based on ab initio calculations, and the results obtained using BSM potential are more compressible. Meanwhile, K-T dependence of temperature Tat zero pressure is investigated. At an extended pressure and temperature ranges, K-T has also been predicted. The properties of MgO are summarized in the pressure 0-200 GPa ranges and the temperature up to 3500 K. (C) 2009 Elsevier B.V. All rights reserved.