Abstract: To deal with the system partition during the phase of testability analysis, this paper presents a fuzzy clustering method for system LRU partition. First the mapping relationship is established between the system structures and system functions attributes; then the components are clustered by the similarity between the components in the logical matrix. The result of clustering by this method makes the LRU in the classes have a crucial role in malfunction of some functions attributes, what is more, each test strategy of sub-function could lead the repairmen locate the fault LRU quickly. From the theoretical analysis and experimental results, the conclusion can been drown that this method could partition the system under diagnosis conveniently. Further more, the plentiful application has been found in engineering practice.