In order to improve the high-voltage performance of organic insulators against flashover breakdown, a novel composite coating capable of conductive manipulation by the introduction of suitable amount of titanium dioxide photocatalytic semiconductor was proposed. This composite coating containing organic silicon, titanium dioxide and fluorophlogopite was fabricated on polyamide substrate by the brushing method. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectra (FT-IR) and impedance analysis were employed to characterize the coating. Experimental results show that the composite with a very low dielectric loss at high frequencies was well-dispersed and adhered to organic substrate. A nanosecond pulse vacuum flashover test revealed that the insulation strength of nanocomposite coating had a 31.85% increase compared with standard polyamide, implying that a new mechanism could govern the electrical properties of the composite insulator adjusted by the photoconductivity of nano titanium dioxide, in which the mitigation of electron accumulation improves the rate of anti-flashover.