This thesis proposed a community public opinion analysis system which integrates text analysis and data mining methods. Our purpose is to estimate the users’ emotions from their comments of FB fan pages and forums. First, the system crawls the users’ comments from Facebook Pages, Mobile01 and PTT. Then, it eliminates the redundant segments to filter the advertising and useless comments so that only the meaningful comments will preserve. From the rest of these comments, the system will extract domain keywords and define the attributes which contains 5W (who, why, when, where, what) and 4S (positive, negative, neutral, ridicule) to construct a sentiment decision tree. Then, implement FP-Growth algorithm to record the path and frequency of each node in decision tree so that the system can calculate the probabilities of positive and negative sentiment. In conclusion, by targeting a domain our system can obtain the topic phase and its sentimental comments, and perform these result with hypertree infographic.