Based on the RUSLE model, this paper analyzed the ecosystem's soil conservation function and its spatial distribution in Lancang River Basin. This Basin could be one of the regions having the highest ecosystem' s soil conservation capability in China, with an annual ecosystem's soil conservation amount being 2.36 x 10(10) t x a(-1) and the soil conservation amount per unit area being 1453.72 t x a(-1) per hectare. The total amounts of the N, P, and K conserved in soils were 5.74 x 10(7), 3.07 x 10(7), and 3.75 x 10(8) t x a(-1), respectively, and presented an increasing trend from upstream to downstream. Among the ecosystems in the Basin, forest ecosystem had the highest soil conservation capability, followed by grassland and farmland, while desert ecosystem had the lowest one. The soil conservation capability of the ecosystems was linearly increased with the increase of vegetation coverage. Averagely, a 10% increment in the vegetation coverage could result in a 35.3% increment in soil conservation capability. To rationally increase the vegetation coverage by reliable ecosystem management based on local conditions would make good effect in preventing soil erosion and maintaining soil nutrients in the Basin.