The invention discloses a solar stepped heat collection and stepped power generation system and a power generation method thereof, and belongs to the field of solar energy photo-thermal utilization. The system is mainly composed of a solar stepped heat collection system and a stepped power generation system. The stepped power generation system comprises a stirling engine power generation circulation subsystem and an organic working medium turbine power generation circulation subsystem, wherein the stirling engine power generation circulation subsystem and the organic working medium turbine power generation circulation subsystem are arranged in a stepped manner. The stepped heat collection system comprises a tank type light-condensation heat collection device and a disc type light-condensation heat collection device, wherein the tank type light-condensation heat collection device and the disc type light-condensation heat collection device are arranged in a stepped manner. High-temperature gas generated by the stepped heat collection system is used as the heat source of a stirling engine and an organic working medium turbine which are arranged in a stepped manner. In the stepped heat collection system, an air feeding device feeds the gas to the tank type light-condensation heat collection device and the disc type light-condensation heat collection device in sequence for heating so that high-temperature air can be produced. The stepped power generation system achieves stirling power generation circulation through the high-temperature gas produced by the heat collection system first, and then heats an organic working medium of the organic working medium turbine through waste heat of the gas so that Rankine power generation circulation can be achieved.