This study investigates the demulsification and dehydration of aging oil under ultrasonic irradiation. The research explores the experimental laws of water content variation at different transducer input powers and characterizes the microscopic topography, particle size, and components of oil samples before and after ultrasound irradiation. The results show that ultrasonic cavitation effectively destabilizes the oil-water interface, leading to droplet collision, agglomeration, and settling, achieving a maximum dehydration rate of 98.24%. Microscopic and particle size analyses reveal that ultrasonic irradiation reduces droplet size, increases droplet spacing, and enhances droplet distribution uniformity. Component analysis indicates an increase in heavy components after ultrasonic treatment, suggesting that demulsification and emulsification may coexist under ultrasonic irradiation. The study concludes that ultrasonic cavitation can effectively demulsify and dehydrate aging oil, and further research is needed to optimize the ultrasonic parameters and understand the underlying mechanisms.This study investigates the demulsification and dehydration of aging oil under ultrasonic irradiation. The research explores the experimental laws of water content variation at different transducer input powers and characterizes the microscopic topography, particle size, and components of oil samples before and after ultrasound irradiation. The results show that ultrasonic cavitation effectively destabilizes the oil-water interface, leading to droplet collision, agglomeration, and settling, achieving a maximum dehydration rate of 98.24%. Microscopic and particle size analyses reveal that ultrasonic irradiation reduces droplet size, increases droplet spacing, and enhances droplet distribution uniformity. Component analysis indicates an increase in heavy components after ultrasonic treatment, suggesting that demulsification and emulsification may coexist under ultrasonic irradiation. The study concludes that ultrasonic cavitation can effectively demulsify and dehydrate aging oil, and further research is needed to optimize the ultrasonic parameters and understand the underlying mechanisms.