A mixed working medium low-temperature refrigerating cycle system driving an ejector through waste heat comprises a drive pump, a steam generator, the ejector, a condenser, a gas-liquid separator, a first returning heat exchanger, a second returning heat exchanger, a first throttling valve and an evaporator. A mixing working medium liquid-phase component is pressurized through the pump and then enters the steam generator to become high-temperature and high-pressure gas, and the high-temperature and high-pressure gas enters the ejector to eject the mixing working medium throttling refrigerating fluid; the gas enters the condenser to be cooled into gas-liquid fluid, the gas-liquid fluid is separated, a gas-phase component enters the returning heat exchanger throttling valve, the low temperature is generated, the heat of the gas-phase component is absorbed by the evaporator , the gas-phase component enters the returning heat exchangers, the temperature is reset, and then the gas-phase component is ejected by the ejector. The liquid-phase working medium is divided into two parts, one part is throttled and enters the returning heat exchangers to provide precooling, the working medium and the gas-phase working medium are mixed to be ejected by the ejector, and the other part enters the pump to be pressurized to serve as ejecting fluid to finish circulation. According to the mixed working medium low-temperature refrigerating cycle system, the high-temperature and high-pressure steam generated by waste heat is completely utilized for driving the ejector to eject the throttled working medium, and therefore efficient, energy-saving and low-temperature refrigerating can be achieved.