Cracking furnace is an important equipment in ethylene plant, and cracking gas pipeline, featured by large diameter, high temperature and complex working conditions, is one of the key pipelines in cracking furnace. This article briefly summarizes the cracking gas process. Based on the engineering example of a new ethylene plant, the layout of cracking gas main pipe, branch pipe of each furnace, cracking gas valve, decoking valve and purge pipeline is introduced, and the key design points and principles of cracking gas pipelines, the piping layout and the pipe support design scheme are explained.