Abstract: High-voltage hold-off insulator stack is the most crucial component in pulsed power system while applying pulse forming line and pulse compress technology to generating several MV voltage output. The voltage potential distribution mechanism of several radial insulator stacks was studied. An optimized insulator stack configuration was acquired based on static electric field analysis program, and designing method of radial resistor is proposed. Results showed that much uniform electric field distribution of insulator stack was obtained by using grading rings together with the electrical contact of grading rings and radial resistor, the radial resistor becomes the key to the performance of insulator stack. With an applied voltage of 4.5 MV and a duration of 100 ns, the electric field of triple point and Martin were about 25 kV/cm and 120 kV/cm respectively, lower than the theoretical flashover value.