Abstract: The application of on-line coke cleaning technology in the furnace of 1.2 million t/a delayed coking device in Urumqi petrochemical company is introduced. The problems and countermeasures during the process and the effect were described. The surface temperature of the furnace tube decreases by more than 80 ℃, and 500 m3/h fuel gas consumption are saved due to the application of the technology. The life time of the furnace is effectively prolonged, meeting the three year overhaul period. The main factors affecting coke cleaning are: difference of high and low temperature of tube， rate of heating and cooling temperature，decoking process time, thickness of coke in furnace tube. The changes of gas consumption at constant temperature, surface temperature difference of each furnace tube, and temperature difference between the furnace tube surface and branch outlet can be used as a success criterion for the process.