Ethylene cracking furnace is a major energy consumer in ethylene plant. By increasing air preheating temperature, the fuel consumption of cracking furnace can be reduced and the thermal efficiency can be improved. However, while reducing fuel consumption, changes in the air preheating temperature also affects the operation of cracking furnace. This article takes the design of a 150 kt/a cracking furnace in an ethylene plant as the example, analyzes and studies the influence of different air preheating temperatures on the main process parameters. The calculation results show that with the increase of air preheating temperature, fuel consumption can be effectively reduced and thermal efficiency can be improved, but at the same time, some problems will emerge such as a decrease in flue gas volume and a reduction in ultra-high pressure steam production. Some relevant suggestions are proposed for the application of air preheating technology in cracking furnaces.