The commutation failure of the valve group will happen in the hierarchy where the single voltage level of Alternative Current (AC) system fails. It will also happen in another hierarchy in Ultra-High Voltage Direct Current (UHVDC) transmission project with hierarchical connection. The interaction between hierarchies of AC and DC system will also lead to successive and multiple commutation failures in the process of fault recovery. A commutation failure control and recovery strategy based on real-time fault detection and determination is presented, which can judge the fault state, the voltage level when fault occurs, and the duration of the fault. Start control strategy only when the instantaneous fault of AC system is serious. The times of automatic restart can be reduced by preventing early restart in the recovery process. The hierarchy is changed to bipolar half-voltage operation mode when serious failure occurs permanently in a single-hierarchy AC system. Based on Changji-Guquan UHVDC transmission project, a simulation model of UHVDC transmission with hierarchical connection is established in PSCAD/EMTDC. Meantime, various fault situations are set up. The results show that the proposed strategy can effectively reduce the number of successive commutation failures, accelerate fault recovery and improve transmission reliability. This work is supported by National Key Research and Development Program of China (No. 2018YFB0904700).