Conductive composite comprised of carbon black and waterborn polyurethane was prepared by latex blending. It exhibited sensitivity to non-polar solvent vapors and polar solvent vapors as a result of the microphase separation structure of polyurethane. By studying the electrical response and absorption behaviors of the composite in low vapor pressure, a model based on Flory-Huggins principle was proposed to discuss the specific performance of the composite, including selective sensitivity, influences of vapor pressure and test temperature. Interaction between solvent and matrix polymer was proved to determine the maximum magnitude of response of the composite.