Some conductive MWNT with different loading was filled in epoxy resin through the dispersion technique of surfactant-decoration, high-intensive shear mixing, and bath sonication process. This kind of conductive functional resin coating was then simply brushed on a FRP sheet surface. The electrical conductivity of the cured nanocomposite coating was acquired by four-electrode method to explore the percolation threshold and piezoresistive effect. The change in its longitudinal strain of the coating and FRP sheet was simultaneously sampled under three-point bending. Results reveal that, at the onset percolation threshold (2.0%), the nanocomposite possesses superior piezoresistive effect with high strain-sensitivity (up to 27), which favors to health monitoring to FRP structure used as a novel self-sensing coating.