For a distillation column under practical operation, the reflux ratio, feed location, flowrate of the top or bottom products are all very important parameters. Using the process simulation package ASPEN PLUS to solve mass balance, heat balance and phase equilibrium equations of a distillation column, the relationships between feed location and content of key components, feed location and heat loads, reflux ratio and content of key components, reflux ratio and heat loads, flowrate of the top product and content of key components, and flowrate of the top product and heat loads, can be determined. With the specifications for the content of key components as constraints, the optimal feed location, reflux ratio and flowrate of the top product can be determined. The o-xylene (OX) column in a xylene plant is optimized as a case study in this paper. Under the optimal conditions the heating utility for the reboiler can be reduced by 20%, OX can be produced by 0.8% more, and operating cost can be reduced by 2,336,000 yuan per year.