A novel and simple strategy to prevent swelling, disintegration, cracking and peeling-off of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) film in water was developed. This strategy was based on the film of a conducting polymer, poly(acrylic acid modified EDOT-co-EDOT):PSS (poly(EDOT-co-EDOT-AA):PSS). The film had high soaking stability, good adhesive ability, and high flexibility, which are crucial to maintaining long-term electrode stability in water of the PEDOT:PSS film. The most widely studied novel carbon nanomaterial, graphene, and a unique and versatile clay nanomaterial, halloysite, were introduced into poly(EDOT-co-EDOT-AA):PSS aqueous dispersion to prepare organic polymer–inorganic nanocomposites. Use of poly(EDOT-co-EDOT-AA):PSS film and its composite films as electrode coatings enabled long-term high performance of the film electrodes and provided high electrode stability and high adhesive ability. The structure, optical, flexibility, conductivity properties and morphology of poly(EDOT-co-EDOT-AA):PSS and its composites were systematically investigated. The performance of poly(EDOT-co-EDOT-AA):PSS film and its composite films, and their electrodes in sensing applications was also evaluated. The as-prepared electrochemical electrodes displayed high electrocatalytic activity in the detection of epinephrine, tryptophan, maleic hydrazide, and vitamin B₆, as well as high sensing stability. The results indicated that poly(EDOT-co-EDOT-AA):PSS and its composites had potential applications for various electrode coatings.