In the production of pure terephthalic acid, a tiny amount of reactant p-xylene and byproduct methyl acetate may enter into the acetic acid dehydration system through the feed stream. In this work, considering p-xylene and methyl acetate as feed impurities in the industrial acetic acid dehydration process using n-propyl acetate as entrainer, the binary parameters for the UNIQUAC model of the quinary system were obtained by correlating the phase equilibrium data from experiment and literature. Based on the physical property model, the distillation character of this quinary system in the industrial dehydration process was analyzed, the models of the dehydration process via heterogeneous azeotropic distillation were developed, and the process simulation was conducted with Aspen Plus. The simulation results of key parameters agree well with the process data with the errors within +/- 6%. Based on the process model, the sensitivity analyses of the bottom water content, reflux flow, two side-draws, and two heat feeds were conducted, which can provide theoretical guidance for the operation optimization study in future work.