Based on 1:200 000 stream sediment survey and partial results of soil survey, the authors summed up geochemical backgrounds of As and Cd and their anomaly distribution in different media and all types of soils and bedrocks, analyzed their enrichment regularity and sources. It is concluded that the background content of As and Cd in the soil is higher than their content in the stream sediment, and is by far higher than their average content in the Earth's crust. As and Cd content is highest in lime soil and limestone, being 1.5 times of their average soil content in Yunnan Province. The background content tends to rise with the increase of pH. The high geochemical anomaly is consistent with the karst area. Seven anomaly zones of As and twelve anomaly areas of Cd were delineated, with the most outstanding anomalies all located in southeastern Yunnan where desertification is severely developed. Heavy metal anomalies of As and Cd are mainly derived from the bedrock of high background content (carbonate rock), and the main reason for its enrichment is that carbonate soil with high pH and high CEC is heavy and viscous, its organic content is high, the migration rate of As and Cd decreases and their remaining content increases, resulting in high enrichment of soil As, Cd content in some areas of Yunnan Province where carbonate rock is well developed.