A FCC mechanism model was used to predict the effects of propylene promoter in a 3.0 Mt/a FCCU.The FCC mechanism model was developed based on one set of commercial FCC data without using the promoter,and was modified by using another set of commercial FCC data with 3m%promoter in the catalyst inventory,and the calculations by means of this simulation model were performed to predict the data of the FCC unit containing 4m%promoter in the catalyst inventory.The test results showed that the calculated values agreed well with the data obtained from the commercial FCC unit,in which the deviations of calculated product yields versus the actual product yields at the commercial FCC unit were equal to 1.74 percentage points for gasoline,2.59 percentage points for diesel,1.50 percentage points for dry gas and LPG,and 0.28 percentage points for coke.The proposed method regarding the development of a simulation model and modifications to the model for commercial FCC unit was feasible. A FCC mechanism model was used to predict the effects of propylene promoter in a 3.0 Mt / a FCCU. FCC Mechanism model was developed based on one set of commercial FCC data without using the promoter, and was modified by using another set of commercial FCC data with 3m% promoter in the catalyst inventory, and the calculations by means of this simulation model were performed to predict the data of the FCC unit containing 4m% promoter in the catalyst inventory. the test results showed that the calculated values ​​agreed well with the the data obtained from the commercial FCC unit, in which the deviations of calculated product yields versus the actual product yields at the commercial FCC unit were equal to 1.74 percentage points for gasoline, 2.59 percentage points for diesel, 1.50 percentage points for dry gas and LPG, and 0.28 percentage points for coke. proposed method for the development of a simulation model and modifications to the model for commercial FCC unit was feasible.