The exact evaluation of the condition of large power transformers is an important research subject in electrical engineering field，and the key task is to assess the operation condition of power transformers based on state parameters．However, the exact assessment result has not been acquired until now according to traditional assessment methods．A new assessment method based on the Analytic Hierarchy Process was proposed in order to overcome the disadvantages of traditional condition assessments based on "acceptance" or "overproof"．Firstly, the equipment state and its evaluation hierarchy model were analyzed. The health value was employed to quantitatively describe the running state degree of power transformers, and the weight vectors of all evaluation hierarchies were discussed by using the analytic hierarchy process methodology with the experiences of experts. The valuation model for power transformer's health state based on the analytic hierarchy process methodology was built. The practical operational results have shown that the proposed assessment model and method are correct and effective.