Enhancing the coordination between functional departments of a firm is an effective method to overcome the difficulties brought by information autonomy , and can improve the effectiveness of decision making. Therefore this paper puts forward a new decision2making method , called“decision2making method through coordination be2 tween functional departments based on dynamic information interaction”. In the method , all functional departments of a firm is divided into one dominating department and other non-dominating departments ,and every department has the opportunity to become a dominating department or non2dominating department , and general decision-making models are put forward to these two conditions respectively. The information exchanged in the process of coordinating is well-defined , and the process of decision-making through coordinating is also described step by step. All above make up a theory basis for constructing a decision support system based on coordination between functional depart2 ments