Terrestrial water cycling encompasses mainly three factors, including precipitation, evapotranspiration and runoff, and dry or wet of the climate mainly depends on precipitation and evapotranspiration. Crop evapotranspiration is a major index to take into account in assessing climate drought degree, crop potential productivity, vegetation water consumption, and water resources supply and demand balance. And it may also provide a scientific basis for calculating crop water requirement, evaluating agricultural water resources, and developing reasonable irrigation schemes. It is generally believed that rising temperature will speed up surface evapotranspiration, and aggravate surface drought degree, while precipitation will increase will supplement the soil with water and relieve the surface droughtiness to a certain extent. So research and analysis on precipitation and evapotranspiration is of certain reference value to evaluating surface soil moisture conditions. The Huaihe River Basin, located between the Yangtze River basin and the Yellow River basin in the east part of China,, is a transitional zone between the north and south climates in this country, and belongs to the warm temperate semi-humid monsoon climatic region. Because of its special geographical position, the complexity and variability of its climate and frequent subjection to the impacts of convergence of cold and warm fronts from the north and south, precipitation varies frequenly and sharply, thus often leading to occurrence of droughts or flooding in this region. In the context of global warming, whether the climate in this region will change as affected by the factors mentioned above, how it will change, and what the development trend will be, are problems that call for systematic research. So analysis of changes in surface soil moisture content of the region will be of some practical significance. The precipitation data of the region monitored day by day were calculated and analyzed, and potential evapotranspiration and relative humidity at each station during that period of time were worked out using the Penman-Monteith formula. The interannual and decadal variation trends of precipitation, relative humidity index and potential evapotranspiration were analyzed through statistics. The analysis mainly used wavelet function of the Matlab software for cycle analysis and the Mann-Kendall test to analyze saltation of the variation trends. In which UF stands for clockwise standard normal distribution curve, while UB for counter-clockwise standard normal distribution curve. AcrGIS 10.1 was used to analyze spatial distributions of precipitation, potential evapotranspiration and relative humidity index The interpolation method used the inverse distance weighting(IDW) method, which set the distance between the interpolation point and the sample point as weight for calculate of weighted mean. The advantage of this method lies in being relatively intuitive and rapid in operation and applicable to dataset with sample points evenly and densely distributed. On such a basis, further study was done on characteristics of the spatio-temporal distribution and variation trend of soil moisture regime in the region, so as to provide some reference or basis for precautions to prevent flood, drought and other disasters in the Huaihe River Basin. Results show that: (1) in temporal distribution, the precipitation displayed an almost invisible slowly rising trend, and within the past 53 years, it showed 6-year primary cycles and 14-year secondary cycles, while in spatial distribution, the precipitation showed standard latitudinal difference, being relatively high in the south and low in the north; (2) the potential evaporation was on a downward trend in temporal distribution and in the past 53 years, it showed 11-year primary cycles and 4-year secondary cycles, while in spatial distribution, it displayed a trend mostly reverse to that of the precipitation; (3) in temporal distribution the relative humidity index was also on a slowly rising trend, with steady fluctuation range and frequency, while in spatial distribution. the relative humidity index in most of the region followed the same trend as the precipitation showed; and (4) the variation of the surface soil moisture regime of the region was the result of the combined effect of various meteorological factors. It is not difficult to draw the conclusion that precipitation is a positive factor and potential evapotranspiration a negative one affecting soil moistureregime.