To achieve a more accurate assessment of the transformer condition is of great significance for the reasonable maintenance strategies. Aiming at the transformer complex fault mechanism and the difficulty of objective assessment, a method of transformer condition assessment based on A. J. Klee method and extension hierarchy is proposed, which transforms transformer multi - parameter synthetic evaluation into single - object decision. First, this paper established the hierarchical index system, and divided the condition grade. A. J. Klee method calculated the weight of the indexes. Extension hierarchy determined the comprehensive evaluation level, and the results compared with the fuzzy analytic hierarchy process (FAHP). The case verified the feasibility of the method applied to the evaluation of transformer status. This mothed provides a new assessment strategy for transformer insulation condition maintenance.