This article addresses defects of current Web information extraction technology such as low accuracy, low coverage, and manual intervention required, proposes a novel extraction algorithm of web medicine information. The algorithm sets up a three-dimentional semantic dictionary by introduction of the semantics technology, masks the isomerisms of the web page contents and structures, and at the same time, taking advantage of the fact that the attributes of the target medicine tend to have a character of aggregation, designs a way of intellectually locating and extracting the target information based on the theory of information entropy. Through related experiments proves that the algorithm is able to reduce the requirement of manual intervention of the information extraction, and has a high accuracy and recall rate. The application of this algorithm can automatically, comprehensively, and accurately obtain Internet medicine information in real time, offers abundant basis of supervision for the medicine supervision department, and therefore has a significant practical meaning of normalizing medical e-business and ensuring secure medication.