Through formalized analysis of the situation of network and the target of fault diagnosis, a new method—FTFD for network troubleshooting based on fuzzy event is proposed. By introducing situation-detection function, FTFD can characterize complicated fuzzy fault with accurate mathematics conversion, and "abnormal degree" can be defined by the vector of probability with belief functions. The method can effectively reduce false positives and negative positives. It aims to be applied to real-time fault diagnosis. The operational prototypical system demonstrates its feasibility and gets the effectiveness of real-time fault diagnosis.