Abstract:  The influence of operating severity on the heavy components of oil vapor, especially the distillate above 550℃, resin and asphaltene in the oil slurry, were investigated in a technical scale riser FCC pilot plant. A correlation between the operation severity and the distribution of heavy components and products was established. The results show that with the increase of operation severity, the content of the distillate heavier than 550℃ and the resin and asphaltene in the oil slurry are decreased obviously. Up to a certain limit, the yield of light oil changes little with the increase of the operation severity; however, it may decrease rapidly when the operation severity exceeds this limit. The operation severity correlation obtained in this work may provide proper guidance for controlling the operating condition to obtain a desirable product distribution and preventing RFCC disengager from coke formation by decreasing the content of heavy compounds in the oil vapor.