Abstract: Aiming at the problem that the oil yield of 1000×10³ t/a FCC unit is lower when the load is high, by optimizing balance catalyst activity, preheating temperature of feed oil, reaction temperature and second regeneration dense phase temperature, the effect of these parameters on the total oil yield was researched when the feed load was 3200 t/d. The results show that when the balance catalyst activity is 61, the feed preheating temperature is 195 ℃, the reaction temperature is (495±2) ℃ and the second regeneration dense phase temperature is (665±5)℃, the total oil yield reaches 88.9%, over 2.6% than non-optimum one.