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It depends on the spatial and temporal variation of soil and grain yield to implement precision agriculture.Grain yield monitoring on combine harvester is a cornerstone of precision fertilization.The intelligent grain yield monitoring system with the sensors and DGPS, which is loaded on the combine harvester, can get the different blocks' yield and produce the yield map.After that, the decision can be made according to the processing results.Typical mechanisms that have been implemented to monitor grain flow through a combine can be grouped into volumetric flow sensors, mass flow sensors, and indirect measurement devices.Compared with other types of sensor, the principle used in grain flow impact force sensors has the advantage of high accuracy and simple installation on combine harvester.As a result, the impact-type mass flow sensors are widely used in many state-of-the-art yield monitors.In this study, a new grain yield monitor system based on CAN bus technology was developed.The system was consisted of grain flow sensor unit,data acquisition unit, GPS module and LCD (liquid crystal display) terminal.The grain yield data was collected by the grain flow sensor, and processed by the signal condition circuits.And then the grain yield data and GPS signal were transmitted to the control unit by the CAN bus.With the algorithm of grain yield conversion, all the collected data including real-time grain yield, harvest area and average grain yield were displayed on the LCD terminal.Flow sensor unit included grain flow sensor, force impact plate and mounting bracket.The sensor frame was mounted at the top of the clean grain elevator of the combine harvester.When the elevator paddles rotated around the sprocket, the grain was propelled towards a flat impact plate.As grain momentum was lost in the subsequent collision with the impact plate, an effective force was measured by the impact parallel-beam load cell.Along with the calibration relationship between measured force and mass flow rate the output of the impact parallel-beam load cell can indicate the flow rate of grain.Data acquisition unit included power conversion circuit, the sensor signal acquisition circuit,analog-to-digital conversion circuit and CAN communication circuit.It could fulfill data acquisition function, CAN communication function and interrupt handling function.LCD terminal had the function of sensor detecting, the function of GPS information collection, parameter calibration, data display and storage.It could display the real-time grain yield, total yield, average yield and harvest area.In order to evaluate the grain yield monitor system, three experiments which included the static performance experiment of grain yield flow sensor, bench test experiment of grain yield monitor system and dynamic property experiment on combine harvester were carried out.The result of bench test experiment shows that the system error between predicted yield and measured yield was less than 3% and the system could avoid the effect of vibration from the platform, effectively.Field combine dynamic experiment shows that the error was less than 5%.Both the experimental results indicate that the grain yield monitor system could satisfy the need of practical production.