Recovery voltage method (RVM) is to study insulation aging status of power transformer. Based on a lot of test data of recovery voltage, the fuzzy rough set theory is proposed and used to assess the oil paper insulation status of transformer. And the assessment system of oil paper insulation of transformer is constructed. Firstly, the evaluation index of oilpaper insulation status of transformer is identified based on recovery voltage feature parameters. Secondly, the membership function of fuzzy partitioning feature parameters for transformer test data is obtained by using FCM clustering algorithm. Then, the fuzzy attributes are reduced for the assessment table of oil paper insulation statue in accordance with the discernibility matrix, and the assessment rules of oilpaper insulation status are extracted. Finally, the assessment system of oilpaper insulation status is built based on the historical database. The experiments demonstrate that the assessment system is effective and feasible which provides a new solution for the assessment of transformer oilpaper insulation status. This work is of practical value in actual engineering applications.