Currently, numerous small and medium-sized enterprises and the local governments have been in the preliminary stage to develop the public opinion monitoring, and such monitoring task of these aspects is mainly realized artificially. For this reason, a reliable and high-efficient internet public opinion monitoring is urgently required to assist the monitoring of the public opinion. The web crawler technology and the search engine are adopted in this paper hereof to establish a public opinion pre-warning analysis platform being well geared into the requirement of the majority of the small and medium-sized enterprises and local governments. This platform shall set forth different fetching strategies in accordance with the different structures from various types of public opinion information, and the online public opinion data shall be collected by the commonly adopted web crawler. In the meantime, the suitable word segmentation shall be adopted, and the full-text retrieval engine shall be applied to fulfill the searching and index of the public opinion information. Eventually, a vertical searching method is designed in this paper, accordingly realizing the commonly used public opinion monitoring function and the topic monitoring function. Such method can be well adopted in the majority of the small and medium-sized enterprises and the institutions of local government to monitor the public opinion.