This paper presents a principle to discuss the subsonic air ejector.Through a seriesof model experiments

the velocity function of free jet has been found.By appl-ication of fluid mechanical principle to an ejector

calculate the lenght of thefree jet and the pressure concerning mixing chamoer.The problem of how toregulate the free jet is also discussed.It was indicated that the effect of chara-cteristic dimension on character of the ejector under different supply pressure con-ditions

a suggestion is made as to the calculating formulae of the geometric para-meters

it may serse as a reference for the design.The paper also expounded thecase its application in the industry.