This study focuses on the ultrasonic electrochemical mechanical polishing (UV-ECMP) technology for cobalt. First, the process parameters were optimized, and a polishing slurry suitable for cobalt UV-ECMP was developed. Subsequently, appropriate ultrasonic and electric field intensities were determined. Experimental results revealed that, compared to traditional chemical mechanical polishing (CMP) and ECMP processes, UV-ECMP exhibited superior polishing performance under identical working conditions. The “oxidation-complexation-removal” mechanism in cobalt UV-ECMP is elucidated: H 2O 2 drives the anodic oxidation of cobalt to generate a CoO/Co 3O 4 layer, while benzotriazole (BTA) selectively complexes with, protects, and softens the oxide layer. Ultrasonic vibration synergistically enhances the removal of softened oxides via abrasive particles. Interaction mechanisms of the ultrasonic and electric field, as well as their regulation of the dynamic balance between oxidation and removal, were investigated. The voltage significantly influences material removal efficiency by affecting the generation mechanism of CoO/Co 3O 4. Ultrasonic vibration improves mechanical removal through cavitation effects and stabilizes the polishing friction force at optimal power levels, thereby enhancing polishing performance. This research provides a new polishing technique for cobalt.