Lithium has attracted much attention because of its wide application and irreplaceability in the field of new energy. In the past, lithium resource exploration was mainly concentrated on the hard rock and brine type lithium resources, and less work was carried out on the sedimentary-type lithium resources. This paper selected the Yunnan, Guizhou, and Guangxi regions in Southwest China as the research area to study the temporal and spatial distribution characteristics of lithium in rocks and stream sediments, to shed light on the regional mineralization potential of sedimentary-type lithium deposits. The results show that the average lithium content of sediments in the study area is 46.7×10^-6, which is significantly higher than the national background value of 32×10^-6. Taking 57.0×10^-6 as the lower limit of anomaly, 9 lithium geochemical provinces were delineated. The lithium geochemical provinces spatially correspond well to the distribution of proven sedimentary-type lithium deposits. Meanwhile, it is found that the abnormally concentrated areas are closely related to the distribution of some formations with specific age and lithology. The lithium content of the stream sediments in the area is restricted by the lithium content of the rock. In the carbonate-dominated structural units, secondary enrichment of lithium in stream sediments was significant. Lithium enrichment in the stream sediments in the tectonic units dominated by terrigenous clastic rocks is relatively weak. Comprehensive analysis suggests that the formation of lithium anomalous belts in southwestern Yunnan, Guizhou, and Guangxi is restricted by multiple factors including regional rock types, secondary enrichment, and climatic conditions. This study is significant for understanding the mechanism of secondary accumulation of lithium in the southwestern Yunnan, Guizhou, and Guangxi regions and guiding the exploration of sedimentary-type lithium resources.