Speed control system and method of direct current (DC) motor

The invention relates to a speed control system and a method of a DC motor. The speed control system of the DC motor comprises three Hall sensors used for obtaining three Hall signals fed back by a three-phase DC motor and a digital signal processing module used for calculating the actual revolving speed of the DC motor according to the three Hall signals, wherein during the revolving speed control of the three-phase DC motor, the actual revolving speed of the three-phase DC motor is compared with a preset revolving speed, the actual revolving speed is modified according to the comparison result, so that the three-phase DC motor can be stabilized at the preset revolving speed. The stability of the three-phase DC motor can be improved through a closed-loop control mode according to an embodiment of the invention.