© 2015, Science Press. All right reserved. The way that constructs geometry of geological objects and carries out 3D prospectivity research is one of the important and available methods to find concealed mineralization. However, there are currently plenty of problems in 3D modeling for geological objects and quantitative assessment. The difficulty especially lies in constructing 3D geological objects based on calculations of spatial analysis, which are related to mineralization. 3D Buffer Analysis is one of the methods among them. In plenty of 3D prospectivity researches, geologists apply block model of geological objects to express results of buffer analysis. Disadvantages of the way are time-consuming, inexact, and poor visualization effects compared with triangle mess. Meanwhile, the grid mess will produce negative influence on the result of quantitative assessment. This paper proposed a method that is with rapid, exact and triangulated characteristics. Specially, the method serves as a surface model of geological objects. And it includes 4 steps, i.e., voxelization of geological objects, revising 3D Euclidean Distance Transform and calculating signed distance field, extracting surfaces from the field, and buffer surface construction based on DSI algorithm. Meanwhile, this paper applies buffer analysis to 3D prospectivity and carries out contrasting tests in aspects of 3D visualization effect, requirement and goodness of fit by using 3D models that are from different study areas and represent different kinds of geological situations. The result shows that buffer expressed by triangle mess is better due to its block model and advantages in quantitative assessment.