Aiming at the technology actuality of surface flow velocity measurement,a novel noncontact method for measuring surface flow velocity is proposed. Principle of flow measurement is deduced,and the factors that affect measurement accuracy are analyzed. Experimental system is set up. In the cases of three sediment concentrations,flow velocity is measured at 6 different flow rates. The experimental results show that under three different sediment concentrations,the measured flow velocity accords very well with the calibration flow velocity,which proves the feasibility of the theory. It is found that the relative error can be controlled less than 8% under the circumstances of suitable sediment in liquid.