Abstract: The velocity of hill-slope runoff is an important parameter for soil erosion and its prediction, however, there is no special and widely used instrument for runoff velocity measurement. Therefore, it is very significant to investigate the method and measurement of runoff velocity. On the basis of previous research, a runoff flow velocity measurement system based on cross-correlation and Virtual Instrument was improved from redesigning the photoelectrical sensor and experiment platform. The optimal distance between sensors, the distance between sensor and water flow surface and the runoff velocity experiment was investigated. The result indicated that the optimal distance between sensors is 5mm and the optimal distance for surface is 9mm. The measurement system is suitable for sediment contents of 0～400 kg.m-3 and for slope gradients of 0～25°, the measured result showed the highest relative error of runoff velocity is 3.61%, which indicates the accurate measurement of the system. This measurement system provides a quick and accurate method for runoff flow velocity measurement.