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Based on the analysis of 13year acid rain data from four monitoring spots in Jiangsu, it is concluded that the annual mean number of acid rain days, the occurrence frequency of acid rain events, and the annual mean amount of acid rainfall in Jiangsu tend to increase gradually from north to south. The frequency and amount of acid rainfall show obvious annual and seasonal variation characteristics. The number of acid rain days and the monthly variation of acid rainfall exhibit a parabolashape distribution. According to the parallel analysis of pollutant concentration and meteorological factors before acid rains, the variation regularities of pollutant concentrations and meteorological factors during acid rains in Nanjing are studied, and the favorable conditions for acid rains are summed up that the preceding pollutant concentration: NO2≥0.04 mg/m3，PM10+NO2≥0.085 mg/m3，SO2+NO2≥0.08 mg/m3; at 850 hPa, southwest winds prevail and southeast winds take the secondary place; wind velocities are less than or equals 12 m/s; there exists an inversion layer under 900 hPa. Base on these findings, the method of acid rain potential forecast in Nanjing is presented and forecast verification is conducted.