Taking the unbalanced current correction of AC filter protection system in Yan Huai HVDC project as the object of study, the structure of the high-voltage capacitor bank and the principle of unbalanced protection are introduced. The importance and significance of unbalanced current correction are clarified. It is unreasonable to point out that the initial unbalanced current used in the traditional method does not fully take into account the fluctuation of its phase and amplitude. In view of the randomness of the initial unbalanced current, the principle and characteristics of LMS adaptive filter are introduced, and its implementation in HCM3000 platform are given. The key parameters of filter are researched and given, and the method of application in specific engineering is expounded. The engineering data verify the rationality of the design and the superiority of the performance. This work is supported by National Key Research and Development Program of China (No. 2016YFB0900600) “Operation Control and Protection of Large-scale AC/DC Hybrid-connected Power Grid”