Electro-induced deformation of water droplets is a complex physical phenomenon that involves coupling electric and fluid fields. It is commonly found on the surface of insulator fittings and equipment high-voltage equalizing rings after rain. Efficient and fast numerical simulation methods are the foundation for revealing the physical mechanisms of raindrop deformation and corona excitation. This article addresses the common problems of long calculation time and complex convergence in the numerical calculation of three-dimensional electric fluid models; a numerical simulation method based on field equivalence is proposed. Starting from the principle of light deflection, a water droplet deformation observation platform based on the shadow method is constructed. The effectiveness of this method is verified by comparing numerical simulation and experimental shooting results. The research results indicate that the relative error between the electric field constructed by this method and the original electric field is within 0.01%. The spray morphology of water droplets obtained from numerical simulation under positive polarity DC voltage agrees with the experiment. By comparing the width and length of the water droplet root, middle, and head, it is shown that the relative error between numerical simulation and experiment is within 10%, verifying the effectiveness of the simulation method in this paper. At the same time, while ensuring convergence, the calculation time is reduced from 8 hours to 1 hour.