Abstract: In order to developing a large feed flow monitoring system of the tangential-axial grain combine harvester, a grain flow sensor calibrating test-rig was developed. Scraper elevator was adopted on the test-rig, and the inclination angle of the elevator was 75°-90°. After the grain being fed into the grain tank, grain flow rate could be controlled by adjusting the opening gap of the flapper during the test. By using the National Instrument DAQ data board, a multi-channel data acquisition system based on graphical programming language LabVIEW was designed, which could realized functions, such as the real-time displaying, recording, analysis of signal of the feed grain tank’s weight, vibration signal and grain flow signal wave. Excluding the impact of the external forces, indoor calibration tests shown that grain feed rate had a great influence to the yield estimation accuracy. When the flow rate was very small, the yield estimation error was up to 6.55%. The average error of the dynamic grain weighing was 4.02% and the average yield estimation error was 4.24%, which could meet the requirement of the large feed flow monitoring system. The designing of this test rig provides a development platform for the grain flow sensor.