Abstract: In order to grasp the occurrence law of acid rain in Taiyuan, and then provide a scientific basis for carrying out environmental weather forecasts and acid rain prevention, the observational datum from 2001 to 2012 were used to statistically analyze the variation characteristics and affecting factors of acid rain in Taiyuan. The results showed that: the annual average precipitation pH value of 12 years was above 4.5, which indicated that weak acid rain/non-acid rain occurred, and was likely to rise year by year. There were obvious seasonal variation patterns in both the frequency and acidity of acid rain, which revealed that the acid rain pollutions were more severe in summer and autumn, while lighter in spring and winter. In addition, the climatic conditions had main effect on the acidity of precipitation. For example, the acid rain frequency reached the peak when the daily precipitation accumulated to heavy rain level or the speed of ground wind was lower than 0.2 m/s; besides, the inverse temperature under low level facilitated the occurrence of acid rain.