Nowadays, many megaton ethylene plants have been built and put into operation in China. It is crucial to improve the marginal benefits of ethylene plants and win market competitiveness. The calculation of marginal benefits of ethylene plant should take into consideration the raw material input cost, the product revenue and the variable cost, and the variable cost consists of auxiliary material cost and fuel power cost. This article discusses the costs of auxiliary materials, fuel and power. Through methods such as original design, process adjustment and equipment modification, the consumption of catalysts, solvents and additives as well as raw and auxiliary materials can be reduced, and the energy utilization efficiency can be improved. It is expected to save 10% of the comprehensive costs, thereby improving the marginal benefits of ethylene plants.