In this paper, the writers discuss the principle bases and metheds for classifying forests. Two methods for classifying forests are suggested as follows( 1 )The classifying method according to forest communities.This kind of classification of forests are based on the characteristics of forest communities. A typological system of five categories is proposed which, in sequence, are forest type, group of forest formation, forest formation, group of forest association and forest association.( 2 )The classifying method according to synthetic factors.This kind of classification of forests are based on both the use and constructive species of forests. A tentative typological system for 64 forest types in Jiangsu Province is suggested.A comparison between these two classifying methods shows that the synthetic method is superior to the other one.