Abstract: It is important to study the drought-flood variation in the arid Northwestern China for regional development and disaster prevention. This work reconstructs the Regional Comprehensive Drought-flood Index (RCDI) series in arid Northwestern China and relevant provinces, based on the drought-flood grades series of 19 sites in the arid Northwestern China. The RCDI series shows that the drought is a major hazard during the last 539 years. It is also found that the drought happened more frequently in the western and high altitude areas than the eastern and low altitude areas of arid Northwestern China. The paper analyzes the fluctuation characteristics of the RCDI series by Empirical Mode Decomposition (EMD) method. The results show that the variations of drought-flood in arid Northwestern China have six quasi-periodic fluctuations which are 2.5a, 7.5a, 13.1a, 25.7a, 77.0a, and 134.8a, respectively. The results also show that the trend of the regional drought severity decreased in the last 539 years.