Abstract: In view of the problem that exceeding the limited seeding quantity is hard to be detected in the use of the rice drill, seeding detector was researched and developed. The detector takes keyboards to set seeding quantity and errors, adopts the infrared photo tube as its detection sensor, employs single-chip microprocessors AT89C51 to collect and process signals and uses display to show the seeding quantity on the spot. When the seeding quantity surpasses the preset number, the sound-light alarming device gives an alarm automatically. The detector bears several characteristics as follows: (1) high precision and reliability; (2) ability to inspect seeding quantity of many rows simultaneously and expansibility; (3) simple structure and convenience; (4) low cost; (5) wide scope of application. The result of experiments shows that all the properties and indexes of the detector have met the expected standards. The detector achieves automatic seeding detection for rice drill, which serves to realize precise direct seeding and improve the production and income.