Abstract: Based on the thought of hydraulic radius separated method,a new computation formula for open-channel resistance segment is created. The influence on flow resistance of flexible vegetation,which is submerged on bed surface of the open channel,is explored and analyzed. A three-dimensional-acoustic Doppler velocimeter is used to measure the velocity near the wall. Measurement of velocity in indirect method is used to determine the tangential stress on the wall. The hair of palm is used to imitate the vegetation. Under the condition of different heights and densities,a series of flume experiments are carried out. The vegetation roughness is used to express the vegetation resistance and the vegetation height and density is used to express the roughness of bed surface. By the regression analysis to experimental dates,the conclusion is that the vegetation roughness increases along with the increase of the vegetation height and density;the bigger the roughness of the vegetation,the more approximate to the vegetation height its numerical value. Empirical relationships between them are fitted and then the computation formula of vegetation resistance is derived.