Soil conservation service, as one of the most important regulating services provided by ecosystems, guarantees the ecological security and sustainable development of a region. We quantified the soil conservation service of ecosystems in Hainan Island using the InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) tool, so as to have a knowledge of its spatial characteristics and impact factors, which could be used for its preservation and ecosystem management then. Our results showed that, the amount of soil preserved by ecosystems of Hainan Island was approximately 8.16×10⁸ t, and the average capacity per unit area was 247.28 t·hm^-2·a^-1 for the entire region. With regard to the spatial pattern, the central part displayed a much higher capacity than surrounding areas in general, which could be confirmed from the comparison of soil conservation capacity between inside and outside of Mountainous Area of Central Hainan National Ecological Function Conservation Area(NEFCA). Consequently, this NEFCA could be considered to be making a great contribution in preserving soil conservation service in Hainan Island. We also found that, the soil conservation capacity differed widely across various ecosystems, with a descending order from shrubs, natural forests, to grasslands, rubber plantations, pulp forests, tropical plantations, paddy lands, dry lands, mangroves, and shelterbelts. Natural ecosystems were generally found to perform better than artificial ones in terms of conserving soil resource. Besides natural factors, economic development, population explosion and farmland expansion are important factors influencing soil conservation service. Indicators such as gross regional product per area, GDP of primary industry per area, population density and area ratio of farmland, showed a negative relationship with soil conservation capacity(P＜0.05), while area ratio of rubber plantation showed a positive relationship with soil erosion rate (P＜0.01). In conclusion: (1) the central mountainous area was so important for erosion control and ecological security maintenance in Hainan Island, that it should be protected carefully; (2) natural forests performed much better than rubber plantations and dry lands in soil conservation, although their economic benefits went the opposite way. Ignorance of ecological benefits ought to be prohibited and preservation of natural forests should be strictly and continuously implemented; (3) traditional agriculture should be transformed to intensive one, so as to increase both productivity and ecological benefits of farmlands; (4) the economic development and population explosion in Hainan Island might impair soil conservation service of ecosystems, as a result, tradeoffs should be made to realize sustainable development.