Photonic networkonchip (PNoC) has been a new trend and example for next generation multiprocessor system. Microring resonator（MRR）is the key component in PNoC. However, MRRs are sensitive to environmental temperature and prone to be faulty. Therefore, how to detect a MRR fault is a key problem. An approach based on fault check graph is proposed. An Nport photonic router is modeled as a complete weighted directed graph called preFault Check Graph, and MRR model is created. By the complete weighted directed graph and fault simulation, the proposed method is established with fault check graph and MRR model. The experimental results prove that the proposed approach is effective with the single fault simulation and double fault simulation.