Abstract: Flow measurement is a key technique of agricultural water management in irrigation areas. At present, various types of flow-measuring devices are available for open channels, but few of them are suitable for field use. Parshall flume has a high accuracy but with a complex structure and high cost. This paper presents a modified Parshall flume that has a flat base, simple structure, and lower cost. This new flume is 774 mm long with a throat of 51 mm wide, and it is easy to carry around and install in the field. Its application range of discharge is 6-20 L/s of a single flume and up to 36 L/s of double flumes. We have taken water level measurements at 11 cross sections under 16 different discharges and obtained by data fitting an empirical formula of discharge versus inflow water depth for the conditions of free outflow. Relative to the measurements, the error of this formula is -0.11% on an average and 7.06% in maximum. Analysis on the variations in Froude number and specific energy at different control sections along the flume under different discharges shows that the critical depth occurs at a cross section near the rear end of the throat, which indicates that the throat length is appropriate.