Aridity index (AI) is a typically reliable indicator of the wet and dry degree in a region, which is widely used in geography and ecology research, and is often involved in global change research. In this study, based on the data from 530 meteorological stations during 1961- 2014 in China, potential evapotranspiration was derived using the FAO-56 Penman-Monteith formula, then AI was calculated using potential evapotranspiration and precipitation and analyzed with the Mann-Kendall (MK) trend test, abrupt change test and wavelet analysis. The conclusions were obtained as follows: 1) The AI in China generally shows a significant decreasing trend during 1961-2014 with significant spatial differences. This holds true for the northwestern region and Tibetan region. A weak decreasing trend of AI is shown in the southern region, while a non- significant increasing trend of AI is shown in the northern region. An abrupt change of AI in China occurred in 1986 according to the MK abrupt change test. 2) According to wavelet analysis, there is a primary 28-year period of AI in China and in the northern and northwestern regions, 29-year period in the southern region and 26-year period in the Tibetan region; meanwhile, there are different secondary periods in different regions. 3) Potential evapotranspiration and precipitation are two major factors influencing the spatial and temporal variation of AI. The decreasing trends of AI in China and in the northwestern and southern region were caused by the decrease of potential evapotranspiration and the increase of precipitation, while the decrease of potential evapotranspiration and precipitation resulted in the non-significant increasing trend of AI in the northern region, and the weak increase of potential evapotranspiration and the significant increase of precipitation resulted in the significant decreasing trend of AI in the Tibetan region. 4) The spatial distribution of AI in China shows obviously opposite pattern with precipitation, with larger AI in the northwestern region and smaller AI in the southeastern region. AI in the northern region is relatively smaller, except in its middle area where a relative larger AI is presented due to the relative smaller precipitation and larger evaporation. AI in the southern region is the lowest in China due to the great amount of precipitation, while AI in the northwestern region is the largest in China due to the small amount of precipitation and strong evaporation. Due to the highest elevation in the Tibetan region and a relatively high quantity of precipitation in its eastern area, AI in the Tibetan region gradually increases from the east to west.