The temporal information of alarm messages is not well employed in currently used analytic models for power system fault diagnosis and， as a result， the diagnosis results may not be unique and hence indefinite especially for complicated and multiple faults. In order to solve this problem， a new analytic model for power system fault diagnosis is developed that makes full use of the temporal information of alarm messages and employs the concept of the dynamic related path. The temporal relationship of the actions of protection relays and circuit breakers in modern power systems with multiple kinds of protection configurations can be rationally represented by the model developed， and definite diagnosis results obtained for complicated and multiple faults. Fault events that occurred in an actual power system are used for demonstrating the model proposed.