Results of calculation indicate that the bubble & dew points may be reduced extremely , but the relative volatility rises slightly and the separation of them is affected hardly by decreasing pressure . and this article puts forward more reasonable modifying suggestions after analyzing numerically in detail the common method of determining the position of sensitive plate in distillation tower and finds out something unsatisfactory about it 计算结果表明,减压可大大降低乙苯?苯乙烯物系的泡、露点,但相对挥发度增加甚微,对其分离的难易程度几乎无影响;对常用求取精馏塔灵敏板位置的方法进行了详尽的数值分析,对其不合理性提出了改进措施。