This paper presents the classification of saline soil method，based on knowledge discovery and decision supporting rule base systems using remotely sensed data and GIS The geo science expert thoughts and expe riences to GIS data mining resulied from classificafion。f saline soil and monitoring secondary soil salinization are introduced．In the study，we construeted perfection knowledge discovory rules which are applied to the North China Plain．The resulting rules are used to improve knowledge discovery systera performance．