Abstract: The ultra-high voltage converter transformer, as the core equipment of the ultra-high voltage direct current transmission system, its insulation performance determines the operational reliability of the system, and the loss level affects the transmission efficiency and energy-saving effect. This article analyzes the core influencing factors of the insulation performance of the ultra-high voltage converter transformer, common failure mechanisms, as well as the main types and causes of losses. It studies the key technologies for insulation improvement and loss optimization, and proposes feasible technical solutions, providing support for design, manufacturing, and operation and maintenance work, and helping the system achieve efficient, safe, and stable operation.