In modern society，false information is likely to both interfere with social public life and cover up the truth.To some extent，microblog is an information platform of rumors.On the other side，microblog has the ability to identify information by filtering error messages.As a “scavenger” and “goalkeeper”，the microblog plays an important role to fight with rumors.This paper tried to investigated the undergraduates’ cognitive of microblog rumors.Taking the “Weibo refutes rumors” and the “Rumor Mill” as examples，it analyzed the information purifying in microblog，suggestion was given at the end of this paper.