Abstract: Based on a dry-wet (DW) index series of last 531 years at 48 stations, we divided the study area into three regions: Area Ⅰ covers North China and the east of Northwest China; Area Ⅱ covers most of the Yangtze River basin; Area Ⅲ covers South China and the Southeast coastal region. The evolutional characteristics of the mean value segments of the DW index series for each area were studied using the power spectrum analysis, the filtering method, and the BernaolaGalvan algorithm. The results show that the frequency of DW transition in the drought-intensive period of the last 130 years, has increased in Area Ⅰ, not obviously changed in Area Ⅱ, but decreased in Area Ⅲ, in comparison with the other two earlier historical droughtintensive periods. In the drynesswetness transition periods, abrupt change points were relatively concentrated, i.e., the climate was unstable, and various climatic extreme events were likely to occur. Based on the period analysis results of the DW index, we found that the current dry epoch started at about 1920 in Area Ⅰ with severe droughts recorded from the late 1970s to the early 1980s, might last for about 50-70 years in this century, and then a DW shift will take place; while the current wet epoch in Area Ⅱ may also continue in the next several decades. Comparing DW variations of Area Ⅰ, Ⅱ, and Ⅲ with the Northern Hemispheric tree ring data, and the Pacific decadal oscillation index, we also found that DW variations in the three areas were to some extent associated with Northern Hemispheric climate change. DW variations in Area Ⅰ were positively correlated with temperature changes, but the correlations in Area Ⅱ and Ⅱ were relatively worse; and the Pacific decadal oscillations might to different extent impact the DW shift in the three areas. It was found from the above analyses that the occurrence probability of various categories of dryness duration index is an exponential function of running window length. Dryness/wetness scale factor was defined as the reciprocal of the characteristic value of the exponential distribution, and its calculations show a bandlike fluctuation distribution wherein the value of the factor increases northwards, with a mean value 1.87/1.66 in Area Ⅰ, 1.62/1.54 in Area Ⅱ, and 1.82/1.71 in Area Ⅲ. The dryness/wetness scale factor is able to quantitatively describe the persistent character of regional dryness/wetness, therefore it can be used to effectively detect the clustering of dry/wet events and the abrupt change of DW index