The invention provides a low temperature heat source thermoelectric conversion system using a blend refrigerant, comprising an evaporator, sprinkler, a first heater and a second heater are successively arranged from the top down in the evaporator, a hot well containing a blend refrigerant is connected to the sprinkler through a pipeline with a booster transfer pump, a steam dryer is arranged at the upper part of the evaporator, the steam dryer is connected with an intake end of a turbine through a pipeline, the turbine is connected with a generator, and an exhaust end of the turbine is connected with a mixer through a pipeline, a reflux device is arranged at the lower part of the evaporator, the reflux device is connected with the mixer through a pipeline, and the mixer is connected with a condenser. The invention further provides a low temperature heat source thermoelectric conversion method using a blend refrigerant.