Reconfigurable computing is a new computing paradigm and acts as an efficient approach for intensive computing applications. But designing reconfigurable computing system is still a great challenge because its architecture is quite different from traditional computers. Formal methods are usually regarded as a competent candidate to model such system at the early design phase. Thus an object oriented Petri net is proposed to model reconfigurable computing systems in this paper. The formal definitions of object oriented Petri net are presented in details. Subnet is adopted to indicate the instance of objective. The basic rules of subnet partition are discussed as well. And techniques of mapping objects to reconfigurable platform are discussed. The features of the mentioned object oriented Petri net for designing reconfigurable systems are summarized finally.