Abstract: Water droplets on the composite insulator surface will distort the electric field on the surface so as to cause corona discharge and accelerate aging of the electric field. Based on the distribution of water droplet and characteristic of electric field on the insulator surface, we first built the model of sheath and shed and finite element simulation model. We employed the solar blind ultraviolet imager to study the influence of water droplet characteristic on corona and flashover voltage. Then we applied the theory of strong electrolyte aqueous solution to analyze the variation of the relative dielectric constant of water droplets with different NaCl addition. The electric field characteristics, corona onset and flashover voltage of the model were studied under the assumption of electrostatic and current fields. We finally studied the influence of water droplet number, volume and location on the electric field characteristic. The results show that, with the increasing conductivity, the corona onset voltage increases by 14% while the flashover voltage decreases by 8.4%. The maximum electric field increases by 2.5%～40% with the increase of the number of droplets. As the volume of droplet increases, the corona onset and flashover voltage of the model decrease by 23% and 25%, respectively. The corona of the shed and mandrel model starts at the sides and top of the water droplet, and the former is 32.5% lower than the latter. This paper provides new ideas for the research of insulator water droplets.