Abstract: Although the hybrid on-load tap changer (OLTC) maintains the advantages of arc free switching and high reliability, its mechanical structure is easy to be damaged and the electrical stress is complex, which means it is difficult to realize the electromechanical coordination control in ultra-high voltage (UHV) scenarios. In this paper, a novel topology derivation and switching strategy of OLTC for UHV converter transformer was proposed. Based on graph theory, the basic network structure and combined structure of tap changer were obtained by analyzing electrical network. Then, the network structure was transformed by using topology derivation methods, and network equivalent transformation. Considering the feasibility and economy comprehensively, the tap switch topology meeting the actual engineering demand was obtained. Taking the OLTC based on star combination structure as an example, the topology derivation process was introduced. The working principle of the six operation modes and five switching actions and trigger conditions for realizing arc free switching were investigated. These theoretical results are in good agreement with simulation ones, indicating that the whole arc free switching process of on load tap changer is only 40ms, and the loss of transition resistance is low. Therefore, the proposed method is conducive to solving the problems of arc burning, additional loss and electromechanical coordinated control of hybrid OLTC, and has high engineering application value.