Abstract: To achieve the target of ultra-low emissions, the original defogger was replaced with a tube bundle precipitator in the 670 MW coal-fired units. In this paper, by tuning the electric fabric filter bypass opening and desulfurization spray level system operating mode, the overall coordination cleaning efficiency of desulfurization system was tested under various working conditions. According to the test results, the tube bundle type dust collector exhibits higher efficiency under high-load conditions. However, under low load conditions, the efficiency drops down drastically and the slurry droplet concentration goes up. Especially, the spray layer operation mode has great impacts on the dust washing effect.