In order to improve the demulsification effect of the high-solid dirty oil with strong stability,the process of ultrasound combined with demulsifier agents(UCD)was employed,and using water content of demulsified oil as the evaluation index,at the condition of 0.15 g/L water-soluble demulsifier SP3 and 0.15 g/L oil-soluble demulsifier AR304,the effect of ultrasound on dirty oil demulsification was investigated systematically. Without ultrasonic assistance,the demulsifier agents alone had no obvious demulsification effect,and the dirty oil was basically in a state of emulsion. By contrast,as the dirty oil was processed by UCD,the water content in oil layer could be decreased from 54.8%(without ultrasonic)to 10.2%,realizing three-phase separation of water,oil and solid. Meanwhile,UCD could decrease solid particle size,ensuring the solid particle separated from oil phase easily;and the contact angle of water on the surface of solid particle was lower than 90°,indicating that UCD could enhance the surface wettability of solid particle. Furthermore,UCD still could decrease the content of resin and asphaltene in dirty oil, promoting the transfer of chemical agents and ultrasonic energy,and reducing the stability of dirty oil,thus achieving demulsification,dehydration and solid removal effectively. The optimal ultrasonic condition was achieved as follows,the ultrasonic power was 500W,the frequency was 22 kHz and the treating time was 10 min.