A driving device of a brushless DC motor for a fan includes a protection circuit, a storage circuit, a control circuit and a bridge circuit. The protection circuit is electrically connected with an auxiliary power. The storage circuit electrically connected with the protection circuit receives the auxiliary power. The control circuit is electrically connected with the protection circuit and the storage circuit. The bridge circuit electrically connected with the control circuit has a first switching unit, a second switching unit, a third switching unit and a fourth switching unit. The first and second switching units are coupled with one end of a motor coil. The third switching unit and the fourth switching unit are coupled with the other end of the motor coil. The first switching unit is electrically connected with the third switching unit, and the second switching unit is electrically connected with the fourth switching unit.