The combination wave generator is used mainly for surge protective devices or electromagnetic compatibility test. The output voltage wave

the output current wave and the output equivalent impedance （it is named virtual impedance Z） are important characteristics of CWG. According to IEC standard

the output waveforms

which include the 1.2/50 μs open voltage wave or the 8/20 μs short current wave

should be generated by CWG under the condition of Z=2 Ω. The paper aims to decide the parameters of CWG circuit through the circuit calculation. Firstly

from the CWG equivalent circuit differential equation

a set of charts for selecting circuit parameters are elicited

and according to these charts

the circuit parameters of CWG are chosen. Secondly

the designed circuit is simulated and developed

the tested results prove that the error is less than 6% and 8% comparing the simulated waves and the tested waves with the IEC standard respectively. It is verified that the method of calculation is correct.