The equation of state which combines Peng-Robinson EoS and the association term of SAFT model was presented for describing thermodynamic properties and phase behaviors of associating fluids. The resulting EoS(Peng-Robinson-Plus-Association) is not cubic with respect to volume and contains five pure compound parameters. 5-parameters of pure chemical compounds were estimated with correlations of both saturated vapour pressures and liquid volumes for alcohols, primary amines, carboxyl acids and water. A method to reduce the number of adjustable pure compound parameters from five to three was considered, and then the 3-parameters EoS model was obtained. This 3-parameter model maintained the good correlations of saturated vapour pressures and liquid volumes. Additionally the equation of state proposed in this work was applied to calculations of vapour-liquid equilibria for the binary mixtures containing associating chemicals, the result showed a good agreement with experimental data for all binary mixtures except for the ethanol/water system, examined in this work.