Abstract: In order to improve the soft switching and dynamic response characteristics of the traveling wave tube high voltage converter, the load characteristic of a traveling wave tube is analyzed, and a full bridge LLC resonant converter with a multiplier rectifier is designed. The working principle, modeling and designing methods of the LLC converter are given based on self-sustained phase shift modulation, especially the soft switching in transient condition and the designing guide of control parameter are analyzed. By simulation, the zero voltage switching in the load mutation condition is proved, and the dynamic response characteristic can be improved by changing the control parameter adaptively. By experiment, the typical wave form of LLC converter is further analyzed based on self-sustained phase shift modulation, and the experiment results show that the soft switching can be implemented.