RF superconducting (SC) cavities are more frequently used in particle accelerators with excellent performance which cannot be substituted by normal conducting cavities. The surface status of superconducting cavities directly affects the properties of the cavity. In order to improve the accelerating performance of superconducting cavities, Peking University made researches and developments on a “dry treatment method” on the surface of SC cavities. It uses argon ion cleaning technique in ultra-high vacuum. Compared with the traditional wet methods (Chemical polishing and electrical polishing), dry method has special advantages. It might become a new surface treatment method to improve the performances of SC cavities. Further researches are in progress.