Aiming at the multiple solutions and misdiagnosis problems for fault diagnosis based on the analytic models for power systems, an analytic method for fault diagnosis based on association rules is proposed. By analyzing the uncertainty about the protective relay action, circuit breaker action and the alarm information, an evaluation index of diagnoses is proposed. The complete diagnoses of faults are obtained by using the analytic method. Considering the probabilities of the above mentioned uncertain elements, the optimal diagnosis can be drawn from the complete diagnoses obtained based on the evaluation index. The effectiveness of the proposed method is verified by the cases of fault diagnosis.