Abstract: Aridity index, used as an important parameter to measure regional dry and wet conditions, has become an important climatic indicator in global change research, especially widely applied in the climate change, drought and desertification research. Dry and wet changes of regional climate affect the local socio-economic and agricultural production severely, therefore attracted extensive attention and study. Hebei Province locates in the semi-arid areas, researching the temporal and spatial variation of surface aridity index there, determining the detailed climatic regionalization, will be helpful to mitigating the adverse effects of droughts and floods. The surface aridity index in Hebei Province is calculated from 1970 to 2007 on the basis of meteorological data in 48 stations, so as to investigate the impacts of climate change on surface dry-wet status. The aridity index is defined as a ratio of potential evapotranspiration to precipitation, and potential evapotranspiration is computed using FAO Penman-Monteith model. The spatial characters of aridity index are addressed by adopting Kriging interpolation, providing some decision-making evidences for the local government of Hebei Province.The results indicate that the variation of annual aridity index, potential evapotranspiration and precipitation could be divided into two periods: 1970-1985 and 1986-2007. Values of aridity index decrease generally in the period from 1970 to 1985. The decrease in potential evapotranspiration is greater than the reduction in precipitation, induced by a decrease of wind speed and hours of sunshine, particularly. The climatic tendency of aridity index is negative (-0.1/10 a), and its average value is 2.34. By contrast, the values of aridity index increase generally in the period from 1986 to 2007, which is attributed to the increase of potential evapotranspiration, caused by the significant increase of air temperature. The climatic tendency of aridity index is 0.14/10a, and its ave rage value is 2.32. Obviously, the ascent rate of yearly aridity index after 1986 is greater than decline rate of that before 1986.From 1970 to 1985, the higher values region of aridity index is located in Sangyang Basin and plateau of western dam in Zhangjiakou, mainly involving Xuanhua, Yangyuan, Huaian, Wanquan, Huailai and Zhuolu County. The range of aridity index is 2.81-3.39, and the higher values center is located in Yangyuan and Huailai County. Inversely, the lower values center of that is located in southwestern Chengde, northern Tangshan and middle-northern Qinhuangdao, mainly involving Luan county, Qian'an, Qianxi, Zunhua, Qinglong, Funing, Lulong and Xinglong county. The range of aridity index is 1.27-1.60. The overall trend of aridity index gradually increase from eastern to western, indicating that the surface wetting conditions of the eastern region is better than those of the western. Compared with the situations during 1970-1985, the increase and decrease trend of surface aridity index in Hebei Province is similar in 1986-2007. The decline region of aridity index is located in the majority of north-eastern part of Hebei Province. The decline trends of aridity index of sourthern Fuping and Laiyuan County in Taihang Mountain are significant, where the reduction value is 0.3. Inversely, the aridity index in the Kangbao, Shangyi, Zhangbei and Guyuan County in plateau of dam increase by 0.1, and it increase 0.1-0.2 in the region from southern Qinhuangdao to southern Handan, in eastern and southern Hebei respectively.