Equilateral-triangle configuration iron core with secondary coil divided into 40 stages, each stage is three-phase full-wave rectified and outputs 30 kV in the design of high power high voltage DC generator, which in series output 1.2 MV/A with energy efficiency of 95% and leakage impedance of 21.7%. Configuration of none-filter capacitance and starlike/trangular connection mode were applied with ripple factor less than ±4%. The whole generator was encapsulated in a steel cylinder filled with highly purified SF6 gas as insulation medium at pressure 0.8 MPa and maximum electric field less than 130 kV/cm, with special cooling system and operating temperature of SF6 controlled less than 60 ℃. Gas-filled coaxial transmission line structure was adopted for high voltage output. All the technic