Electrostatic precipitators (ESPs) have been widely applied in air combustion power plants. Due to the different characteristics of dust removal between oxy-fuel and conventional combustion conditions, an experimental study has been carried out in this study to evaluate dust removal. Fly ash samples collected from a 35 MW oxy-fuel combustion test platform were analyzed, and the tests of fly ash resistivity and fly ash composition were carried out. Meanwhile, the difficulty level of dust removal was evaluated through different evaluation methods. The difference of the fly ash resistivity under air combustion was further understood. The difficulty level evaluation of dust removal by an electrostatic precipitator under oxy-fuel combustion is easier than that under air combustion in a certain temperature range, and the results of different evaluation methods are consistent. Through research and analysis, the design and selection of an ESP under oxy-fuel conditions can refer to the method of conventional air combustion, and the technical guidance for engineering applications is supplied.