Abstract: Causes of abnormal catalyst fluidization in the regeneration system of RFCC unit at Hainan Petrochemical Company were analyzed based on operation experiences and basic theory of solid particles fluidization. It was found that lower catalyst bulk density, overload of unit and partial interrupted of semi-regeneration slope pipe were the main causes. Countermeasures were proposed and put into practice, such as optimizing catalyst formula and production technique to improve fresh catalyst bulk density and shape; increase the bulk density of regenerated catalyst by using some magnetic separated catalyst; reducing unit load and properly adjusting the main air flow ratio between the 1st and 2nd regenerators, as well as optimizing the pressure differential between reactor and regenerator; adjusting the number of aerating sites and aerating air flow to improve catalyst transfer in slope pipe. Since then, the abnormal fluidization of catalyst in the regeneration system was eliminated.