Karst landscapes in Southwest China may be an important carbon sink after the implementation of ecological engineering. The carbon pool in vegetation plays a more important role in the ecosystem carbon budget than that in shallow soils with a limited carbon savings. However, due to the special nature of the geological settings of the Karst region, the spatial distribution of vegetation has a three-dimensional characteristics of discontinuity and fragmentation, which results in the difficulty in obtaining the belowground section of vegetation. This study examined the influencing factors on spatial distribution of vegetation carbon density in the karst area of northwest Guangxi, China, based on 1377 samples of 13 environment factors investigated in 2010 and the model of radial basis function network. The results show that: the four most important impact factors on the spatial distribution of vegetation carbon density are land type, forest type, forest category and vegetation type, and the significance of standardization above 50% for all of these factors; The second group of important impact factors are rocky desertification degree, humus layer thickness, size class, overall vegetation cover and soil thickness, and the significance of standardization is about 15%-30%; The least important factors on the spatial distribution of vegetation carbon density are location, slope, aspect and elevation, and the importance of standardization is only 2%-11%. Our study indicates that, and land type, forest type, forest category and vegetation type changed by human activities are the predominant factors in controlling the spatial distribution of vegetation carbon density, and the impact of topographic factors on are limited. This study suggests that the eco-environment immigration, returning farmland to forests, rocky desertification control measures have positive impacts on the spatial distribution of vegetation carbon density.