For studying the breakdown characteristics of the grading capacitor C

E

（grading capacitor）in the multistage graphite gap under the action of 1.2/50 ms impulse voltage

the equivalent circuit of the capacitor is calculated theoretically in time and frequency domain. The coupling ability of impulse voltage with different values of grading capacitor C

E

is tested and verified. The results are applied to the breakdown characteristic test of impulse voltage wave of multistage graphite gap. It is found that the capacitance of grading capacitor C

E

which is greater than 1 nF

is the most reasonable value. From point of view of resi

dual voltage and overall breakdown time

the sample with relatively low capacitance shows that residual voltage reduces 40% and the overall breakdown time shortens 90% at the amplitude of low impulse voltage and

on the contrary

their performances at high impulse voltage amplitude are better. It is suggested through test and study that the capacitance of C

E

in the multi stage graphite gap shall be between 1 nF and 12 nF.