A new classification algorithm for web mining is proposed on the basis of general classification algorithm for data mining in order to implement personalized information services. The building tree method of detecting class threshold is used for construction of decision tree according to the concept of user expectation so as to find classification rules in different layers. Compared with the traditional C4. 5 algorithm, the disadvantage of excessive adaptation in C4. 5 has been improved so that classification results not only have much higher accuracy but also statistic meaning.