The invention provides a low-temperature heat source thermoelectricity conversion system by means of mixed component working media. The system comprises a steam generator, a spray thrower, a first heater and a second heater are sequentially arranged in the steam generator from top to bottom, and a hot well containing the mixed component working media is connected with the spray thrower through a pipeline with a pressurizing liquid conveying pump; the upper portion of the steam generator is provided with a steam drying device which is connected with the air inlet end of a turbine through a pipeline, the turbine is connected with an electric generator, and the exhaust end of the turbine is connected with mixer through a pipeline; a backflow device which is connected with the mixer through a pipeline is arranged under the steam generator, and the mixer is connected with a condenser. The invention further provides a low-temperature heat source thermoelectricity conversion method by means of the mixed component working media. According to the low-temperature heat source thermoelectricity conversion system and method by means of the mixed component working media, the flow proportion of the steam state working media and the liquid state working media in the backflow device can be accurately controlled so that the liquid state working media can completely absorb and liquefy the steam state working media, therefore, the cycle efficiency of the system can be improved, and the operating conditions of the turbine can be improved; the system is simple in structure, low in cost and convenient to run and operate.