With its rapid development in recent years, microblog has gradually become the storm center of public opinion and one of the mainstream media. However, behind its flourish, microblog also brings hidden problems such as rumor and defraud, pressing for governance and supervision. With content analysis, this paper studies the heated discussion concerning Jiaxin Yao trial on March 23th, 2011 on Sina microblog. We make sampling analysis of the relevant information on microblog, establish three analytical unit—netizen characteristics, information characteristics and propagation characteristics, and do data statistics after coding. Based on data statistics, an multiple linear regression equation is found to describe the degree of transmission of the topic on microblog, thus outlining a preliminary transmission mechanism of public opinion on microblog. Some suggestions on how to use, supervise and guide the internet public opinion are also included in this paper.