Abstract: To effectively monitor quality of corn sowing and reduce occurrence of missed sowing and broken rows, a corn missing sowing monitor based on principle of photoelectric method was designed．Using a 3 mm infrared light emitting tube and a silicon PIN photodiode as sensing elements, a sensor was designed using principle of photovoltaic effect to detect whether seed has passed or not．Main controller was designed with STM32F103 microcontroller as the core．Main controller received signal from sensor through interruption, and when seed passed, it triggerd corresponding internal timer to work or reset．When timer count exceeded 3 s, an alarm signal was generated and displayed on screen．Field experiments showed that within normal sowing frequency range of seeder, counting error was not less than 97%, and detection rate of missed seeding reached 95%．Light intensity and machine vibration have no impact on operation of missed seeding monitor．