Based on the investigation of the differences in process parameters such as crossover temperature and furnace tube temperature during the operation of the No. 6 cracking furnace in the old area of PetroChina Dushanzi Petrochemical Company, it was found that the bellows of four expansion joints of diluent steam pipelines were overstretched and seriously exceeded the design scope. At the same time, the draft tube was seriously deformed and blocked the pipeline, which not only affected the flux of the pipelines, but also led to the fracture and material leakage at the expansion joints if it cannot be found in time, seriously affecting the smooth operation of the plant. In order to completely solve the influence of expansion joint on the operation of cracking furnace, the expansion joint was replaced by straight pipe section by re-calculating the stress of process pipelines and adding part of spring hanger and support, thus eliminating the hidden trouble caused by the deformation of expansion joint of cracking furnace.