Service providers always passively respond to the demands from service objects in traditional information service model. The function and efficiency of service provider are strongly restricted by this kind of passive model. Therefore, we brought up a "Symmetrical and Active Service Model" (SASM) in reference [1]. This article, aiming at the key points of SASM, proposes a system of Ontology-Based Actively Discovering Potential Demands of service objects (OBADPD). In the OBADPD, service provider can determine service objects initiatively by obtaining the status variation; inferring and filtering potential demands of service objects based on some relevant Ontology. In order to describe the process of discovering potential demands of service object, the car life ontology, problem solving ontology and reasoning method in OBADPD are introduced. Finally, some interesting instances are given to show the process.