Abstract: A new molecular thermodynamic model for water is developed in which water molecules are taken as "softened" hard spheres with dispersion, induction and electrostatic interactions. The expressions for thermodynamic functions such as Helmholtz free energy, equation of state and vaporization enthalpy are derived according to perturbation theory. The molecular parameters are obtained by fitting experimental vapor pressure and liquid density data simultaneously in a temperature range of 0-300℃ . Meanwhile the vaporization enthalpy and specific volume of vapor are predicted with a small deviation. Moreover, some molecular thermodynamic models for water are compared. The results show that our model is simple and accurate.