In this study, the change of the surface wetness index (SWI) was investigated in Gansu province using the observed meteorological data from 54 stations during 1961 to 2012. The results showed that bounded by the Yellow River, SWI were different from east to west, in the east of the Yellow River it tended to dry, especially in Longdong area, and in western part it tended to wet, especially in the central of Qilian Mountain. The dry trends in eastern part mainly happened in autumn, especially in September, and wet in western area occurred in winter, especially in December and January. A differentiation equation method was used to attribute the change in surface wetness index to climate variables. The results indicate that except for precipitation, the surface wetness index was most sensitive to the change in relative humidity, followed by sunshine duration, maximum temperature, and wind speed respectively, the minimum temperature has the lowest sensitivity. The actual relative change of SWI was between -30% to 30% in the past 52 years, and precipitation was the dominant factor which contributed -30% to 25% of the change. followed by wind speed with -4% to 12%, the contribution of maximum temperature, sunshine duration and relative humidity were small than others, which caused -4% to 4% changes of SWI.