The capital market has a history of 300 years，which has experienced three stages：scatter to concentration、booming development of exchange system and interactive development between modern OTC and exchange-traded market.In this process，OTC market structure has been changed significantly，and formed diversified and mutiple level structure，which has the trend of convergence to that of exchange-traded market.American OTC market appeared national pink sheet market，the NASDAQ market and OTCBB market successively，and finally formed multi-level market structure；AIM generated in London stock exchange and extended down to the OFEX market through the LSM’s market maker，which is a case of integration.The structure of Taiwan OTC market and Emerging Stock Market is a case that the OTC market is independent to the mainboard market.