When a fault/alarm occurs in a smart substation, the amount of data in the secondary system network is very large. And it is very difficult to locate the fault/alarm location and find reason quickly and accurately. The general Assessment method to secondary device takes the physical device performance as the index and uses the algorithm to evaluate, the logic model in devices is not evaluated. This paper establishes the index system of devices’ logic model and function gather, and completes the logic matrix to judge the function state by using the factors which have an influence to function as the conditions for trigger calculation. The example proves that this method has a great help to fault identification and search.