The 750 kV substations in the Northwest China are mostly located in sandstorm-prone areas. Due to long-term erosion by wind and sand, corona discharge is serious with noise pollution in these substations. In this paper, taking a 750 kV substation as an example, corona discharge in the substation was observed by using ultraviolet (UV) imaging technology. The results of UV imaging show that wind-sand erosion will make the surface of fittings uneven and produce different forms of defects, which will lead to serious corona discharge. In order to study the effect of wind-sand erosion on fittings, three-dimensional finite element model of a certain bay of the substation was established by using finite element analysis (FEA) software, and models of the fittings eroded by sandstorm and smooth models without erosion were adopted respectively in the simulation. Then, the electric field distribution of the substation was calculated, and the electric field characteristics of fittings with different defects were analysed. The simulation results show that defect type, size and position will influence the characteristics of electric field distribution with different laws. The study could provide guidance for the structure design of fittings and the reduction of corona discharge in 750 kV substations.