Modify the Method of Feature's Weight in Text Classfication

In auto text classification,TFIDF is often used when the weight of a term is calculated.The method is easy,only considers the frequency of the feature and ignores the feature's contribution to each class.Aiming at this shortage,we put forward the TFIDF-CHI and use it to modify each feature's weight,read just each feature's differentiation to each class.Then the KNN classifier is used to check its validity.The method is better than traditional TFIDF and proves that the TFIDF-CHI method is feasible.