This paper selected three hot events in 2017，which are “4.14 insults mother killing case”，“the death of a young boy Li Wenxing” and “Jiang Ge incident” respectively. It adopts the case analysis method to figure out the development of Internet public opinion in these three cases. This paper pointed out that Internet public opinion can be divided into four stages，incubation period，development period，peak-hour stage and recession stage. In the incubation period，the sensitive issues and the psychological framework of the netizen will lead to further development of the public opinion；in the development period，the opinion leaders will contribute to the growth and diffusion of public opinion while the cooperation between traditional media and new media helps to push public opinion to the peak；in the peak-hour stage，sense and sensibility coexist in the public opinion and the input of fresh information will lead to fluctuation；in the recession period，as things are solved，issues are scattered or covered by new issues and events that have not been thoroughly solved will become potential public sentiment factors.