This research work developed a model for the MIP riser reactor using the data collected from an industrial MIP unit.Based on analysis of flow patterns in the reactor,three models were established and a comparison was made on each other.The results indicated that Model Ⅲ,which was assumed a plug flow in the first reaction zone and a gas plug flow and a continuously stirred catalyst flow in the second reaction zone,was the best.The results of this research could offer an information and guidance for optimization and development of MIP unit.