By studying the flow resistance of valve core of Venturi constant air volume, the paper discovered that the flow resistance coefficient is the key factor to describe the flow resistance in the operation process of the venturi constant air volume valve core. Therefore,the paper designed the experiment device so as to study the flow resistance coefficient. Through studying the flow resistance and the flow resistance coefficient with different body contraction angles or different valve core positions, it obtained the following conclusions that the flow resistance coefficient and the equivalent diameter express a good power function; the flow resistance coefficient decreases with the increase of equivalent diameter,and the variation extent of flow resistance coefficient increases with the increase of various shrinkage angle.The flow resistance coefficient basically keeps constant under different air volumes of the same position.