Abstract: Presented in this paper is a special working process, long neglected in the snubber circuit of GTO inverters in the mode of PWM.After a complete theoreticl analysis of the specical working process is deduced the formula for the independent current created by the snubber circuit of this process in the main-loop.It follows from the formula that the absorption capacitance must be limited, and the upper limit of the capacitance is calculated. The argument put forward in this paper has been proved by experiments and it will be of important reference value in the design of PWM-GTO inverters.