Power equipment condition assessment is the premise and foundation of power system condition-based maintenance. A power transformer condition assessment method based on fuzzy and evidence theory for 500 kV oil-immersed power transformers is proposed. Some representative parameters in preventive test are chosen as the condition assessment indexes, and all of these indexes are normalized according to ex-factory value and off-limit value. The membership to different condition assessment level of the assessment indexes is determined by fuzzy evaluating method. All the assessment indexes are divided into three sub-evidences, which are DGA, oil test and electrical test. Set information composition of these sub-evidences based on evidence theory, and then the power transformers condition assessment are determined by the information composition results. The effectiveness of the transformer condition assessment model is verified by example analysis of 500 kV power transformer parameters. The assessment model is clear and does’t need a lot of historical data, which offers a new way for power transformer condition assessment.