A Brushless Direct Current (BLDC) motor starting method and device are provided, in which startup noise and vibration and startup failure rate can be reduced using a constant low-speed startup scheme when the BLDC motor is in sensorless startup mode, and PWM duty is also maintained at low level when the BLDC motor starts up, thereby preventing an excessive current from occurring due to desynchronization of the motor at startup, so that it is possible to optimize specifications of an inverter in the BLDC motor. The BLDC motor starts up with a startup speed and a PWM duty of a rotor of the BLDC motor being kept constant, and the BLDC motor switches to sensorless mode if a position of the rotor is detected a predetermined number of times or more during a specific time.