Abstract: The impacts of sever al factors on performance of FC-CU are analyzed including hydrocarbon component s of raw material,refining of straight diesel oil and vacuum residu-um,and h ydro-pretreatment.It is believed that the more content of hydrogen is,the mo re favorable it is for the pro-duction unit.Refining of straight diesel oil c an make profits only when production of diesel oil is in surplus or its price is very low.The economic benefits of refining of vacuum residuum are relatively g ood.The profits of hydro-pretreat-ment of the raw materials of FCC are highe r than that of hydrofining.