This study investigates the demulsification and dehydration of aging oil under ultrasonic irradiation. Aging oil emulsions with high water content and complex components are common in oilfields, making demulsification crucial. Experiments were conducted to explore the effects of ultrasonic power on water content and dehydration rate. Microscopic, particle size, and component analyses were performed to characterize the oil samples before and after ultrasonic treatment. Results showed that ultrasonic cavitation significantly reduced water content, with a maximum dehydration rate of 98.24%. The dehydration rate followed an "M-type" trend with increasing power. Microscopic analysis revealed that ultrasonic irradiation destabilized the oil-water interface, causing droplets to collide, agglomerate, and settle. The study also found that ultrasound may not be irreversible in demulsification and dehydration of aging oil. The mechanism involves cavitation, mechanical, and thermal effects that reduce interfacial tension, destabilize the interface, and promote droplet aggregation and settling. The results suggest that demulsification and emulsification may coexist under ultrasonic irradiation, and that the cavitation effect can effectively achieve demulsification and dehydration. The study highlights the potential of ultrasonic technology for efficient and environmentally friendly aging oil treatment.This study investigates the demulsification and dehydration of aging oil under ultrasonic irradiation. Aging oil emulsions with high water content and complex components are common in oilfields, making demulsification crucial. Experiments were conducted to explore the effects of ultrasonic power on water content and dehydration rate. Microscopic, particle size, and component analyses were performed to characterize the oil samples before and after ultrasonic treatment. Results showed that ultrasonic cavitation significantly reduced water content, with a maximum dehydration rate of 98.24%. The dehydration rate followed an "M-type" trend with increasing power. Microscopic analysis revealed that ultrasonic irradiation destabilized the oil-water interface, causing droplets to collide, agglomerate, and settle. The study also found that ultrasound may not be irreversible in demulsification and dehydration of aging oil. The mechanism involves cavitation, mechanical, and thermal effects that reduce interfacial tension, destabilize the interface, and promote droplet aggregation and settling. The results suggest that demulsification and emulsification may coexist under ultrasonic irradiation, and that the cavitation effect can effectively achieve demulsification and dehydration. The study highlights the potential of ultrasonic technology for efficient and environmentally friendly aging oil treatment.