Abstract: In order to further understand the similarity of hollow cathode discharge, this paper studies whether the positive column of glow discharge can destroy the Townsend similarity of hollow cathode discharge. Two groups of parallel plates with geometrically similar air gaps (proportional coefficient k is 2) were selected for argon glow discharge experiments. The length of the positive column was gradually increased by increasing the pressure. It is found that the glow-discharge voltammetry characteristic curves of the two geometrically similar air gaps always coincide. Based on the two-dimensional fluid model, the glow discharge in the above experiments was numerically simulated, and it was found that the corresponding physical parameters of the two glow discharges always met the proportional relation of similar discharge. Through theoretical analysis and derivation, it is found that the ambipolar diffusion process in the positive column of glow discharge is an allowable process of similar discharge. Finally, it is concluded that the positive column of the glow discharge may not be the reason for destroying the Townsend similarity of hollow cathode discharge(HCD).