An exemplary fan driving system includes a driving device and a MOSFET group. The driving device includes a first adjustable resistor connected between its first voltage signal input terminal and ground, and a second adjustable resistor connected between its second voltage signal input terminal and ground. The MOSFET group includes two N-type MOSFETs and two P-type MOSFETs. The first terminal of the fan is connected to an anode of D1 and a cathode of D3. The second terminal of the fan is connected to an anode of D2 and a cathode of D4. Cathodes of the D1 and D2 are configured to connect a supply voltage. Anodes of the D3 and D4 both are grounded. The fan driving system can effectively discharge off the residual current in the coil of the fan at the moment of the MOSFET group being switched off.