The invention discloses an acetylene gas sensor and a preparation method thereof. The acetylene gas sensor consists of an Al2O3 (aluminum oxide) substrate, a Pd (palladium) metal interdigital electrode and an Au (copper) nanoparticle-modified SnO2 (stannic oxide) nanocrystalline sensing layer. The preparation method comprises the following steps of cleaning the Al2O3 substrate of the Pd metal interdigital electrode, and drying; obtaining an SnO2 nanocrystalline material at room temperature; dissolving chloroauric acid into deionized water to form a chloroauric acid solution, adding the SnO2 nanocrystalline into the chloroauric acid solution, treating by ultrasonic wave, adding ammonia water, and cleaning, drying and calcining a product, so as to obtain the Au nanoparticle-modified SnO2 nanocrystalline material; grinding into microsphere powder; dripping deionized water, and grinding into a pulp; coating the Pd metal interdigital electrode with the pulp, and drying, so as to obtain the gas sensor which uses the Au nanoparticle-modified SnO2 nanocrystalline as the sensing layer and the Pd as metal of the Pd metal interdigital electrode.