The invention discloses a heavy oil emulsifying and viscosity-reducing composition and an emulsifying and viscosity-reducing method thereof. The heavy oil emulsifying and viscosity-reducing composition is prepared from an emulsifier and a nanometer material according to a weight ratio of (1 to 10):1. The heavy oil emulsifying and viscosity-reducing composition has the advantages that the formed heavy oil emulsion has strong stability, the easiness in influence by systems, salt types, temperature, composition of oil phase and the like is avoided, the site maintenance is favorably performed in the heavy oil production and transportation process, the nanometer material and the emulsifier in the emulsifying and viscosity-reducing composition generate the synergistic emulsifying function, and the emulsifying and viscosity-reducing effects of the heavy oil are improved; the nanometer material is friendly to environment, the treatment cost of waste liquid in the heavy oil emulsifying and viscosity-reducing process is reduced, the toxic or harm effect to the human body is greatly lower than the toxic and harm effect of surfactant, and the injury to an operator in the actual use process isreduced.