AIS (automatic identification system) is a new kind of maritime communication and navigation system, it includes navigation information (ship identity, location, course, speed and etc.) which can be automatically exchanged between vessels, vessels and coastal stations. It is an important technology means for avoid ship collision, VTS, tracking line drawing, ship grounding alert, maritime accident investigation, etc. As we know, the precondition and base of the mentioned use of AIS is getting AIS information timely and reliably, and the construction of collecting system based on INTERNET with a certain scale definitely consumes large amount of human, material, and financial resources. So serious study on the sharing mechanism of AIS information is significantly important in avoiding redundant building of collection systems, shortening AIS study and application period, saving resources and promoting collaborative researches. A web-based dynamic IP switch system for AIS data sharing has been developed so that the AIS data sharing server can respond to data accessing requirements only by dynamic IP. This article discusses the structure and basic work flow of this system, principle of Vc++'s accessing the Http page and the realization of the server side and the client side.