Abstract: The runoff plot is a useful means for erosion and hydrologic studies, the measurement of flow rate is the main task of observation from runoff plots. A new system capable of automatic measuring of runoff was developed. The system integrated the components of V-notch weir, data logger, device for data storage and transmission. A laboratory flume experiment was conducted to calibration the discharge coefficient of the integrated weir, and to establish the simplified discharge function. The calibration experiment indicated that the simplified discharge function was correlated with data sets, with the determination coefficient 0.98. Moreover, the impact of exist of sediment in the sediment laden water on the estimation of runoff had been discussed. A calibration model to transform the flow rate of sediment-water mixture to flow rate of water was provided. With capability and reliability of high accurate measurements, this system could be used widely on runoff plots for erosion study.