The supercritical CO2 Brayton cycle has garnered significant attention due to its ability to maintain high efficiency even at relatively lower operating temperatures. This paper proposes a simulation method for fluid networks based on the supercritical CO2 cycle system, which allows for various equipment configurations and parameter settings. The method automatically partitions nodes by inputting equipment parameters. The accuracy of the fluid network simulation results is validated by comparing them with the design values of various supercritical CO2 Brayton cycle configurations. Based on this simulation method, the bypass scheme is adopted to adjust the demand load of the SCMR-15 system and the dynamic characteristics are analyzed. The result shows that the scheme incorporating bypasses at both the reactor and turbine can avoid equipment failures but still experience the reduction of cycle efficiency as demand power decreases.