The present paper deals with an elementary principle of a new measurement of runoff with very low discharge by means of resistance measuring-flow, and the nonlinear Flow-Voltage relationships with the resistance measuring-flow. A method of linearization handling is provided to make the Measuring-Runoff Flume in a better linear relationship. The analysis of dynamic response charactertics of Resistance Measuring-flow Flume is based on system dynamics theory, as a result, system parameters ωn and ζ are obtained for judging regulating-storage of measuring-flow device' The Measuring-flow Flume has been applied to measure small discharge in the Hydro-logic Runoff Laboratory. As it belongs to instantaneous flow-rate measurement method, the runoff hydrography measured is very clear as regards its duration, peak discharge, lag of time, and relevant parameters. In addition, the device has a higher stability of electronic circuit and better signal-to-noise ratio, and the problem of electolytic action at electrodes surface due to impurity of the water has been solved, so it is more convenient to make research of the rainfall-runoff relationship in laboratory. Finally, in this paper a comparison of cumulative sum of hydrography from Resistance Measuring-flow Flume with cumulative water-volume-method is given, and satisfactory results have been obtained.