Fault diagnosis is a challenging issue in complex dynamical networks. In the real-world complex dynamical networks, there exists much uncertain information, such as unknown topological structure and uncertain node parameters. Based on network outer synchronization, an approach to fault diagnosis is proposed for a class of output-coupling time delay complex dynamical networks with unknown node parameters. Output variables are used to construct the controllers. A few conditions satisfying outer synchronization are specified from Lyapunov stability theorem. The proposed approach can be used to monitor the online evolution of time-delay network topological structure. Numerical simulations are given to verify the effectiveness of the proposed approach.