Abstract: Adjustment space of recirculating ratio in conven-tional delayed coking is narrow resulting in a limited unit flexibility.Wuhan Petrochemical Design Institute has in-vested1.2million RMB to modify the delayed coking u-nit by using an adjustable recirculating ratio process flow.The production capacity of the unit was enlarged from400,000t/a to1milliont/a.The adjustable recirculating ratio process flow has the advantages of high fluid yield,low coke rate of production,flexible operation and strong adaptability.