The invention discloses a power transformer state evaluation method based on a rough set-cloud model. The method comprises the following steps: (1) collecting the state quantity data information of a sample transformer; (2) processing the state quantity data by utilizing a cloud model; (3) calculating the weight of the state quantity by utilizing a rough set; (4) determining a state interval score of the state quantity, and calculating the integral score of the power transformer; (5) establishing a cloud model of the state interval score of the power transformer; and (6) according to the interval score of the power transformer and the cloud model of the cloud model of the state interval score, determining a state level of the power transformer. The power transformer can be subjected to state evaluation, and an evaluation process is reasonable, and a result is visual, accurate and reliable.