In order to calibrate the winddirection sensors automatically, an automatic calibration system is developed independently, based on the AVR singlechip computer and the photoelectric detecting technology. The core of the system is the microprocessor ATMEGA16 of ATMEL, which realize the automatic calibration of winddirection sensors through detecting the electric pulses. The system can display the information of winddirection sensors and print the results of the sensor detecting, has the advantages of lowcost, high stability, and low power consumption, and has realized the automation of wind direction sensor calibration.