A hybrid power generation system using a supercritical CO2 cycle includes a steam power generation unit including a plurality of turbines driven with steam heated using heat generated by a boiler to produce electric power, and a supercritical CO2 power generation unit including an S—CO2 heater for heating a supercritical CO2 fluid, a turbine driven by the supercritical CO2 fluid, a precooler for lowering a temperature of the supercritical CO2 fluid passing through the turbine, and a main compressor for pressurizing the supercritical CO2 fluid, so as to produce electric power. The steam power generation unit and the supercritical CO2 power generation unit share the boiler. The hybrid power generation system may improve both the power generation efficiencies of the steam cycle and the supercritical CO2 cycle by interconnecting the steam cycle and the supercritical CO2 cycle.