Abstract: The concept of membership degree of the fuzzy set theory is well suited for the analysis of plant communities,where both abrupt and smoothly continuous distribution variations of plants and environmental quantities are often found. This work is an application of ISODATA based on fuzzy set theory to the classification problem of the grassland community in Songlun Plane,Northeast China. The result shows that the technique is objectively correct and is manipulative compared to the classical methods. In addition,the classification guided by the Minimum Description Length Principle proved that the principle is suitable for this type of classification problems.