Abstract: Poly (3, 4-ethylenedioxythiophene) (PEDOT) was synthesized from 3, 4-ethylenedioxythiophene by chemical oxidation polymerization. A series of working electrodes coated with nanocomposite, made by blending PEDOT powder and functionalized carbon nanotubes (f-CNTS) powder with liquid glue as crosslinking reagent, were applied to the test of saturated vapor containing formaldehyde on the self-made gas sensitive device. Test results indicated that contents of MWNTs polythiophene, and concentrations of formaldehyde had different effects on the structure of the micro gas sensitive response. Meanwhile, compared with the single material, the composite membrane had a better electron transfer behavior, indicating a better gas sensitivity.