In order to solve the difficult problem of oil sludge seum treatment in a refinery, the microwave-ultrasonic method was used to pretreat the oil sludge scum and the reaction products were analyzed. The influence of microwave and ultrasonic on the removal rate of oil sludge scum was analyzed by L25 (52) and L16 (43) orthogonal tests. The process parameters such as microwave time, microwave power, ultrasonic time, ultrasonic temperature and ultrasonic power were optimized. The results showed that the removal rate of petroleum substances in oil sludge scum by microwave-ultrasonic method was high. The removal rate and recovery rate of petroleum substances were 53.23% and 31.03% respectively when the microwave time was 4 min, the microwave power was 252 W, the ultrasonic time was 40 min, the ultrasonic temperature was 70 ℃ and the ultrasonic power was 50 W. The effects of temperature, time and power on the removal rate of crude oil of oil sludge scum decreased in turn. After microwave-ultrasonic treatment, the space between sludge particles of oil sludge scum increased, the sludge surface became rough, the texture became loose, the tight adhesion state of oil sludge was broken, and the contents of petroleum hydrocarbon components C12-C37 decreased obviously.