A fiber counting type rapeseed precision seed metering device seed flow detection system was designed to solve the problem that the accuracy of seed flow detection was reduced as the speed of rapeseed precision seeding was increased. It consisted of an optical fiber counting sensor, a core control module, a step-down module, a wireless communication module, and a Web terminal. The seed flow detection mechanism of the optical fiber counting sensor was elucidated, as well as the particle kinematics theory was used to develop the contact kinematic model of the seed and seed tube, and the sensor's reaction time was also clarified. The voltage signal was created by blocking the optical fiber by sensing the falling seed flow via the optical fiber sensor while the system was operational. The signal was then depressurized, collected, transported through many modules, and integrated with the terminal for display and storage in real time. Huayouza 62 rapeseed seeds were chosen as the test material, and a six-degree space vibration table fitted with a pneumatic precision seed metering device served as the test platform. As test factors, vibration frequency, seed plate speed, and working negative pressure were used. The relative deviation of the coefficient of variation of the displacement consistency was used as the evaluation index, and sensor accuracy tests, detection system performance tests, and field tests were done. The results of the test indicated that the relative deviation of single and double-grain detection test results was no more than 3.67%;the relative deviation between the actual value of the seed quantity in each row and the detected value did not exceed 4.0%;and the relative deviation of the coefficient of variation of each row did not exceed 1.0%. The results of the field test indicated that the relative deviation of rapeseed detection did not exceed 8.0%. The overall error of the system was small, providing a technical basis for future research on the quality evaluation system of precision rapeseed seeding operations.