This paper is concerned with the problem of networked fault detection for the networked control system (NCS). As for the output time delay in the feedback channels for the network between the plant and the controller, so at the controller site, the actual output of current time instant cannot be gotten. This paper makes use of self-adaptive predictor technique of online identification predicting the current time instant output for the known delay τ of the output. A traditional fault detection filter is used for the detect ion. With which we can predict the plant state of the current k time instant at the condition of getting the data of k — τ time instant. The approach can be feasible for the gradual change fault of the plant. The design algorithm of the fault detection scheme was summarized. At last, an example is given to show the approach is feasible.