Given the problems of oil refinery slag sludge ("slag sludge") containing a large amount of dirty oil, complex composition, and challenging to deal with, the pretreatment test of slag sludge produced by Sinopec Jinling Branch was used by ultrasonic means. The influence of ultrasonic power, ultrasonic temperature, ultrasonic time, and ultrasonic frequency on the decontamination rate of slag sludge was analyzed by L₁₆ (4^₄) orthogonal test method. Error analysis was carried out by SPSS 25.0, and the orthogonal experimental results were refined by using the single-factor test. The infrared spectrometer analyzed the change of the composition of the sludge before and after the ultrasonic. The experimental results show that the order of influence factors is ultrasonic power < ultrasonic time < ultrasonic temperature < ultrasonic frequency. When the ultrasonic power is 70 W, the ultrasonic time is 15 min, the ultrasonic temperature is 55℃, and the ultrasonic frequency is three times the removal rate of petroleum substances can reach 32.46%. The infrared spectrum showed that the spectral intensity and oil content of the corresponding peak of oil sludge decreased significantly after ultrasonic. Aromatics, alcohols, alkanes, olefins, and other substances all decreased, indicating that the long chains of petroleum hydrocarbons and the carbon chains of high molecular organic compounds were destroyed. After ultrasonic extraction, the number of alkane substances in the oil decreases, while the amount of alcohol substances increases, indicating that one hydrogen group of an alkane is replaced by a hydroxyl group to produce corresponding alcohol. Compared with alkane, alcohol is more easily degraded by microorganisms. The mechanism of ultrasonic Treatment of scum oil sludge is as follows: through mechanical effect, cavitation effect and thermal effect, the long chain of petroleum hydrocarbon and the high molecular organic carbon chain are destroyed, the viscosity of scum oil sludge is reduced, and the three phases of oil, mud, and water are easily separated, thus reducing the content of petroleum substances in scum oil sludge. The ultrasonic method is a physical method, no additional chemical drug price, the treatment method is simple, can be used as a composite treatment process pretreatment means.