Abstract: In this work, a two-dimensional numerical simulation of the discharge characteristics of helium plasma propagating inside a dielectric tube was performed. A trapezoidal +9 kV pulse lasting 400 ns was applied on a needle electrode set inside the dielectric tube to ignite the discharge. The discharges generated in the tubes with a variable or a constant inner diameter were investigated. The focus of this study was on clarifying the effect of the tube diameter on the discharge structure and dynamics. The comparison of the discharge characteristics generated in dielectric tubes with different diameters was carried out. It was shown that the tube diameter plays a significant role in discharge behavior of plasma propagating in the dielectric tube.