Abstract: The supercritical carbon dioxide (S-CO₂) Brayton cycle is widely recognized as a promising power cycle, where the performance of the S-CO₂ compressor is crucial in determining the thermal efficiency of the cycle. In this study, the effect of the pre-swirl angle on the flow behavior and performance of the S-CO₂ centrifugal compressor with inlet guide vane is investigated by numerical simulation. It is observed that an increase in the absolute value of the pre-swirl angle exacerbates flow separation on the suction side of the guide vane, elevating the total pressure loss within the guide vane section and intensifying flow non-uniformity at the impeller inlet. With the increase of the positive pre-swirl angle, the relative flow angle and relative velocity at the impeller inlet decrease, the expansion of the suction side of the blade accelerates and the flow separation weakens. The large positive pre-swirl angle results in a two-phase flow within the inlet guide vane section under high flow conditions. A reference for the study of inlet guide vane regulation of S-CO₂ centrifugal compressor is provided by this research work.