A hair dryer comprises a fan, a heater, a temperature sensor, and a controller. The heater is disposed at the airflow output end of the fan and used to heat the airflow output by the fan. The temperature sensor is pointed to the hair, receiving the infrared light radiated by the hair to obtain the temperature of the hair, determining the dryness of the hair according to at least one of the temperature of the hair and the rate of temperature variation of the hair, and outputting a corresponding control signal. The controller is electrically connected with the fan, the heater and the temperature sensor, and controlling at least one of the rotation speed of the fan and the heating power of the heater according to the control signal. The above-mentioned hair dryer not only can prevent from hair overheating and hair damage but also can shorten the time for drying hair.