Abstract: The acid rain data of Kunming City for 13 years and meteorological data have been used to analyze the characteristic of acid rain.The results show that the trend of annual acid rain frequency has descended in the early stage and then raised,with the higher frequency of acid rain in flood period,the tallest in September,and the lower in dry season;the trend of severe acid rain frequency is consistent with of the acid rain;the times of acid rain in one day emerges more in night than in daytime with the minimum of times appearing at 19:00;there has the indication of SO2 contents to acid rain before 7 hours;annual acid rain and severe acid rain have better relationship to temperature,humidity,fog day,frost day and wind,but monthly acid rain and severe acid rain all have positive correlation to thunder day.The emergence of the extreme acid rain has relationship to the pile-up of acid material in the air,with longer continuous rainless days or heavy rain before the acid rain appearing.