As worldwide petroleum reserves evolve toward heavier crude oils, crude distillation units encounter historically high coking risk, and this problem is further exacerbated by cutting deeper into the bottom for higher HVGO yield. In this work we aimed to optimize the steam injection condition for coking prevention purpose in refining vacuum furnace. A new technology that injecting steam inside the radiant section was proposed and comparison was made with steam injection at the entrance. Variable steam injection location and rate were examined according different operating cases, and the flow patterns in vaporizing tubes and coking tendency curves were present. All the calculations were performed using the commercial software Petro-SIM and the calculation model was validated against on-site data The criterion was proposed for the optimal steam injection condition. The results showed that steam injection inside the radiant section was superior to the entrance. (C) 2014 Elsevier Ltd. All rights reserved.