Abstract: Based on the low-carbon supercritical carbon dioxide(S-CO₂) cycle test rig designed for the national major science and technology infrastructure project of 'High-efficiency and Low-carbon Gas Turbine Testing Facility' under construction, in order to formulate the startup strategy of the test bed and study the dynamic characteristics of the system startup process, a dynamic model of the cycle system is established by using the modular modeling method, and a specific turbine bypass start-up control strategy is designed. For bypass switching during startup, three strategies are proposed: manual switching, automatic switching, and automatic bypass switching considering turbine rolling. The simulation results show that the manual bypass switch could reduce the relative changes of the outlet pressure of the heater and the flowrate of the compressor. However, the pressure at the inlet of the compressor changes obviously, and meanwhile the control effect of the turbine speed is relatively unsatisfactory. With automatic control bypass switching, it is not necessary to preset the corresponding opening of the valves during the switching. At the same time, it can effectively control the fluctuation of pressure or flow parameters. The maximum relative change in heater outlet pressure is about 5.7% and the maximum relative change in compressor flow is about 16% during the bypass automatic switching control when considering turbine rolling. With the designed bypass switching automatic control strategy considering turbine rolling, the parameter changes in the startup process are more stable and controllable, which can provide a reference for the subsequent commissioning of the test bench.