As an important extreme experimental condition, high magnetic field plays an irreplaceable role in the frontier scientific research, such as condensed matter physics, new materials processing. The main pulsed high magnetic field laboratories in the world are constantly working to generate higher pulsed magnetic field. A nondestructive magnet aimed at generating very high pulsed magnetic field such as 100 T is made up of several coils nested coaxially. The outer coil is in charge of getting a long pulse width background high magnetic field, accordingly the outer coil often has large radius and requires enormous energy. At the Wuhan National High Magnetic Field Center (WHMFC), a novel combined power supply of a 1kV battery bank and a 100 MVA / 185 MJ pulsed generator system is designed. In this paper, firstly consideration of magnet coupling function, the energy, stress and heating of the outer coil, a cascade structure of 24-pulse rectifier and battery with crowbar circuit is proposed. Secondly, based on a logically organizing the discharging sequence of power supply, an operation strategy consisting of rectifier, inverter, de-excitation, freewheeling and the coordination of the power supplies is adopted. Thirdly, safe operation areas of the trigger angle of the 24-pulse rectifier are derived. At last, a series of simulations and experiments (up to 20kA) are carried out, and the design of the combined power supply for high pulsed background magnetic field is valid and feasible.