It is one of the most important information to obtain accurate grain yield for precision agriculture. In order to further improve the accuracy and stability of grain yield monitor system, a new dynamic selfcalibration method which was based on the first generation of photoelectric grain yield monitor system and the principle of quantitative screw conveying was designed. The system was composed of grain volume sensor, unloading grain cylinder speed sensor, grain tank state sensor, data acquisition and processing module, display terminal and error feedback calibration software. In order to verify the accuracy of the system, the simulation test of quantitative screw conveying which was at different rotation speeds and different inclination angles was carried out. In June 2020, the field performance experiments were carried out at Beijing Xiaotangshan National Precision Agriculture Research and Demonstration Base. The performance test results of the unloading speed sensor showed that the error of the unloading speed sensor was less than 2%. Bench test results showed that the error between the monitored value of the system and the actual output value was less than 2.5% at different unloading speeds. There was a linear correlation between the flow rate and the rotational speed, and the correlation coefficient was 0.9937. The field error dynamic selfcalibration experiment result showed that the relevant error was -2.95%~3.13%, which was decreased by 0.45 percentage points compared with that of the measuring device without this system. At the same time, the error fluctuation of the system was reduced. The dynamic selfcalibration system provided a new method to improve the accuracy of grain yield monitor.