The invention relates to a semiconductor gas sensitive element variable characteristic demonstrating instrument which belongs to the technical field of demonstrating instruments. A circuit comprises a resistor, a photoelectric coupler, a triode, a light-emitting diode, a loudspeaker and a U257B integrated circuit. The semiconductor gas sensitive element variable characteristic demonstrating instrument is characterized in that one end of the input end of the photoelectric coupler is connected with a cathode of a direct current power supply, and the other end is connected with an ohm gauge; one end of the output end of the photoelectric coupler is connected with the cathode of the direct current power supply, and the other end is connected with the loudspeaker; the resistor is connected with a QM (Quadrature Modulation) series semiconductor gas sensitive element socket; a variable resistor a is connected with the QM series semiconductor gas sensitive element socket; a base electrode of the triode is connected with a variable resistor b; a collecting electrode of the triode is connected with an anode of the direct current power supply; and an emitting electrode of the triode is connected with the cathode of the direct current power supply by the resistor b. By adopting the technical scheme, the invention has the advantages of visual demonstration and low cost.