To achieve the maximum NOx reduction in coal-fired power plant, excess ammonia is injected into the selective catalytic reduction reactor, which leads to the formation of ammonium bisulfate due to the reaction between ammonia escaping from the selective catalytic reduction reactor and sulfur oxides in the flue gas. Ammonium bisulfate can condense in the rotary regenerative air-preheater, which would adversely affect the safe and efficient operation of the air-preheater. An improved Radian number is proposed to estimate the ammonium bisulfate deposition. The operating conditions or modes of the air-preheater, i.e., rotating speed, air flow bypass, cold-end protection and different splitting fluid sector arrangements, are comparatively studied to analyze the temperature and ammonium bisulfate deposition distributions. To decrease the rotating speed is not a reasonable method for the plugging problem of the air-preheater. The hot air recirculation is not helpful to mitigate the ammonium bisulfate deposition in medium matrix layer. The splitting gas sector arrangement would cause more serious plugging problem, but the splitting air sector arrangements can alleviate the ammonium bisulfate deposition. To increase the air bypass rate is more effective than the splitting air sector arrangements to alleviate the plugging problem. The improved Radian number is more reasonable to reflect the ammonium bisulfate deposition compared with the original Radian number.