Supercritical helium has been considered as an ideal working fluid in a number of design studies for closed Brayton cycle due to its thermal properties. But the low density level of supercritical helium, the characteristics of the small flow channel in the turbomachine and the variable working condition method of the system determine that the compressor may run at low Reynolds number. In this paper, the influence of Reynolds number on supercritical helium compressor rotor is investigated under different conditions by numerical simulation program. Effects of specific heat ratio on Reynolds number sensitivity of supercritical helium compressor rotor are also investigated by comparing the calculated results of different working fluids. Special attention is paid to the relationship between properties of working fluids and efficiency. Then, the equations of efficiency and total pressure ratio for different working fluids are established. The results show that the Reynolds number sensitivity of supercritical helium compressor rotor decreases with the increase of tip clearance and increases with the increase of the specific heat ratio. (C) 2017 Elsevier Ltd. All rights reserved.