The work aims to study a de-painting technology based on ultrasonic compounding of molten salt, so as to remove thick paint on remanufactured end caps. Firstly, microstructure and composition of the paint were analyzed by SEM and FTIR. Composite cleaning mechanism was revealed by combining the laws of molten salt removal and ultrasound removal. Then, on this basis, a composite cleaning test was carried out. In the method of central composite test, with composite cleaning cycle as evaluation index, test data was fitted to establish regression equation and response surface model, and Minitab was used for optimal analysis of such process parameters as cleaning temperature and ultrasonic power, and experimental verification was set up. A clear layered structure was obtained inside the paint, and its main ingredients were organic compounds including ester groups, epoxy groups and aromatic compounds. Besides, composite cleaning mechanism was effect of thermal expansion, chemical, surface tension and ultrasonic cavitation. With the increase of cleaning temperature and ultrasonic power, chemical reaction rate in the cleaning field was increased, ultrasonic cavitation effect was intensified, and composite cleaning capability was enhanced. The shortest cleaning cycle was 4.5 min, optimal cleaning parameters were: temperature 335 ℃ and ultrasonic power 1440 W. Residual volume of surface contaminant was 0.2 mg after cleaning, and changing rate of hardness and tensile strength was 0.83%, 1.68%, respectively. These all meet remanufacturing standards. Ultrasonic cleaning of molten salt can effectively remove contaminants by selecting suitable process parameters, and cleaning effect and mechanical properties meet remanufacturing standards.