A motor driving system includes a controller, motors and motor drivers. In the normal supplying state of a power supply, the controller controls the motor drivers. The motor drivers output driving signals for driving the motors respectively. In an abnormal state or a power-off state of the power supply, one of the motor drivers is set to be a master driver and the others are set to be slave driver. The master driver activates a deceleration energy backup (DEB) function, powers the slave drivers through a common-DC-bus structure, controls the slave drivers, and during deceleration maintains a ratio between frequencies of the driving signals, until all of the motors are decelerated to stop at the same time.