Despite the growing interest in the supercritical CO2 (S-CO2) Brayton cycle, research on the cycle transient behavior, especially in case of CO2 compressor inlet condition variation near the critical point, is still in its early stage. Controlling CO2 compressor operation near the critical point is one of the most important issues to operate a S-CO2 Brayton cycle with a high efficiency. This is because the compressor should operate near the critical point to reduce the compression work. Therefore, CO2 compressor operation and performance data from the S-CO2 compressor test facility called SCO2PE (Supercritical CO2 Pressurizing Experiment) were accumulated. The data are obtained under various compressor inlet conditions. Furthermore, in this study, the validation of the gas system transient analysis code GAMMA was carried out by utilizing the experimental data of SCO2PE. To simulate the data by the GAMMA code, the code was revised to model the compressor performance. A transient case for reduction in cooling event was simulated with the facility and the experimental data were compared to the revised GAMMA code. The revised GAMMA code showed a reasonable performance and demonstrated the potential of the code for being used in a larger scale S-CO2 power system. (C) 2016 Elsevier Ltd. All rights reserved.