According to the specific characteristic of the micro-blog user's interests changing with time, a potential interest discovery method based on fuzzy association rules(PIDFAR) is proposed. It could express micro-blog theme distribution by using LDA topic model, and then use the time weighted method to calculate user's recent interest subject distribution, for mining fuzzy associate rules. That set of association rules to express and discover the general rule of user's interests change over time. Finally, after calculating the similarity between the the associated rule of association rule in the collection and the topic distribution of user's interest, take the high similarity of the latter collection in association rules set to constitute the user's potential interests. Experiments show that the method of PIDFAR can make the process of discover the user's potential interest break away from the limit of user's friends group, and improve the accuracy of the discovery of potential interests of micro-blog users obviously than the traditional method of discovery potential interest based on collaborative filtering technology.