Dongsheng mining area in Inner Mongolia is located in the fragile ecological area. Under the background of global warming and open coal mining, investigation of the variation of surface dry-wet conditions in this region over the past decades is of great importance. Based on the potential evapotranspiration(E₀) calculated by using the Penman-Monteith method,the ratio of E₀ to precipitation was used as aridity index(∅) for the years 1957—2012. The temporal variation, frequency distribution and periodical characteristics were analyzed. And a total derivative method was used to attribute the change in surface dry-wet conditions. The results showed that the annual aridity index was 3.2 with an increase of 0.004 per year. There was a drying trend in summer, while other seasons trended to be wetting, but the trend of four seasons was not significant. Significant periodicities of 18 -25 and 7 – 12 years were examined, and the primary period was 12 years. The recurrence intervals of maximum and minimum E0 were both more than 50 years. An abrupt increase occurred in 1998. Maximum temperature was the main climatic factor affecting the change in surface dry-wet conditions, followed by precipitation and wind speed.