As a special physiognomy in nature, the mountainous region has peculiarities of uncertainty, complexity and multifactor, and digitization and classification should be conducted to find out its specific nature. With the support of spatial analysis and mathematical statistics, four factors were extracted and analyzed on the basis of ArcGIS application characteristics in Sichuan Province. They were absolute elevation, relative elevation, slope and terrain roughness. An integrated classification system for mountainous region was built by statistical methods to generalize these tow factors into two major factors and figure out the critical value of classification. The final classification results for mountainous and non-mountainous regions in Sichuan Province were extracted by using the ArcGIS grid calculator. The extraction results show that this method has reached the accuracy of the classification levels by the traditional method, thus laying the research foundation for realizing 'digitized mountainous region.