With the rapid development of the network, the exploding volume of digital information make it very difficult to use for users. Then, the researches focus on the information filtering technology which can reduce the users burden in the course of obtaining the network information. Firstly, The paper introduce two filtering model ——Boolean model and Vector Space model. After this, the paper give a detailed introduce to the famous information passive service system ——SIFT including its working princip leand filtering kernel. Finally, the paper analysis SIFT’s function and character and point out some defects in the filtering system.