Since the 1960s, Ailaoshan in southern Yunnan has been thought as the boundary of southwest monsoon and southeast monsoon, which significantly determine regional climatic variation as well as other landscape heterogeneities. Through using monthly rainfall data from 1961 to 2007 at all the 11 meteorological stations in the centralsouthern region of Ailaoshan and Wuliangshan, this study first analyzed the spatiotemporal variation characteristics of rainfall in wet season and each month within that period, then discussed the links between the spatiotemporal variation and regional topographical feature and the two monsoons. The rainfall characteristics in wet season and each month showed there existed obvious variation between the southeast part and the northwest part of study area, while the central part had obviously transitional characteristics. Wet season rainfall on the southwest slope of the eastern range of Ailaoshan is far higher than that of the northeast valley (rain shadow) of the eastern Ailaoshan range. But, within both sides of the eastern Ailaoshan range, wet season rainfall decreased gradually from southeast to northwest. Correlation coefficiencies of monthly rainfall between neighbouring stations within the eastern Ailaoshan range always kept high in wet season. But correlation coefficiencies of monthly rainfall between the northwest and the southeast stations showed obviously fluctuation. The interfacing condition of southeast monsoon and southwest monsoon in wet season in this region varied with the development of monsoons. Average onset and shrinkage dates of southeast monsoon are both earlier than these of southwest monsoon. With the onset of southwest monsoon, the interface region of these two monsoons in earlier wet season is the Babian River basin. In June and July, the two monsoons gradually became strong and interface with each other within the whole region. Within the drawback procedure of the southeast monsoon, the interface region of the two monsoons moved to the southern part of Ailaoshan.