Abstract: The successful design of Soil Classification Expert System(SCES) depends on the soil taxonomy that classifies soil types using quantitative data. This paper presents an oriented-object based method to simulate the rational thinking of soil classification experts to make rational rules of expert knowledge, soil diagnostic horizon and diagnostic characteristic theory. The structures of soil classification decision trees and reasoning machine were also discussed to construct the framework of SCES. The GIS was also integrated into the system to provide geographic data and spatial analysis means to implement soil classification.