A 40 kV/6 kA pulsed power supply was designed for the rapid cycling synchrotron(RCS) extraction Kicker magnet of Chinese Spallation Neutron Source. The calculation of the pulsed power supply’s parameters, the design of power supply’s system, the optimization of pulse forming network(PFN) are introduced. A new type of low impedance PFN is also presented. The magnet current pulse waveform was simulated by PSPICE program in the situation of 36.5 kV charging voltage, and the amplitude of the pulse was 5.8 kA. The simulation results show that, with the same PFN section capacitor and inductor, the pulse length of the current is prolonged when more section number of PFN is chosen, while the rise time and flatness of the pulse has no significant changes, choosing the suitable length of transmiss