Abstract: In view of the fact that nowadays the clean coal products contain a large amount of foreign matters. To tackle this problem, and for making better use of coal resources and upgrading of clean coal products, a study is made on extraction of light foreign matters from clean coal using an improved heavy medium vessel which works with water as separation medium. Study result shows that the foreign matters can be effectively removed with the use of heavy medium vessel; the design of the forced discharge mechanism plays a vital role in the process; and the form of flight and selection of flight chain all exert a great influence on the vessel's treating capacity and service life.