Failure cases play an important role in failure analysis. This paper will focus on how to determine the failure mode of the new failure cases from some existed failure cases. First, the fuzzy relationship matrix of each failure mode and unexpected appearance information can be obtained from the large amount of failure cases have been collected. Secondly, the comprehensive evaluation for the new failure cases can be basically evaluated, the evaluation results corresponding to various failure modes can be calculated. Thirdly, the most probable failure modes will be determined through comparison with the threshold. But if more than one probably failure modes existed, Euclidean algorithm will be used to calculate the relative Euclidean distances of the new failure case to each probably failure modes obtained from above. The failure mode to which the new case belongs can be determined through above several steps.