[Objective] This paper proposes a new method based on the Support Vector Machine to monitor online public opinion. [Methods] We extracted fourteen linguistic characteristics of the micro-blog posts and analysed their sentiments with Support Vector Machine. [Results] The precision, recall and F value of the proposed method were 82.40%, 81.91%, and 82.10%, respectively. [Limitations] The size of training corpus needs to be expanded. [Conclusions] The proposed method could effectively analyze sentiments of micro-blog posts.