The supply system in urban mass transit provides power for vehicles. The quick and accurate fault positioning after its failure is worth researching and key for the reference of maintenance personnel, to minimize the duration of power failure. Based on Object-oriented Petri nets (OOPN), this paper proposes Object-oriented Colored Petri nets (OOCPN), which introduces member variables and member methods into OOPN. With OOCPN. the conventional CPN model for topology analysis is modified into an OOCPN model, through the solution of which a gross fault region is located, together with possible miss-trips and error-trips. The result of OOCPN model is then reasoned backwards with protection and action information from human-machine conversation for final fault node and further breaker analysis. The method proposed takes into consideration the peculiarity of protection configuration in supply system, and is subjected to both theoretical analysis and an example case, which proves it practical and efficient.