A 200 kV high voltage switch power supply has been developed, based on softswitching power supply technology and cascading voltage multiplier. Its working principle and structure are presented. The high voltage switch power supply mainly consists of power convertor, intermediate frequency transformer and high voltage multiplier. Its main indices are high voltage up to 200 kV, output current up to 10 mA, working frequency of 20 kHz, high voltage stability of 1%, voltage ripple coefficient of 2% and continuous working time up to 8 h. The performance of the high voltage switch power supply has met the design requirements.