A speed-changing method of bicycle, suitable for controlling a gear ratio of a bicycle, the bicycle has a chain, a plurality of front chain rings, a plurality of rear chain rings, a front electronic derailleur, a rear electronic derailleur, a controller and a controlling switch, the chain is driven by the front electronic derailleur to move back and forth among the front chain rings and is driven by the rear electronic derailleur to move back and forth among the rear chain rings, and the controller stores a gear-ratio table, the speed-changing method of bicycle comprises: triggering the controlling switch to generate a corresponding signal; and controlling the front electronic derailleur and the rear electronic derailleur by means of the controller according to the signal, if the signal is a speed-increasing signal, the controller controls the front electronic derailleur and the rear electronic derailleur to move the chain from one of the rear chain rings to another one of the rear chain rings along a speed-increasing path of the gear-ratio table for increasing the gear ratio and controls the front electronic derailleur to move the chain from one of the front chain rings to another one of the front chain rings at a first switch point of the speed-increasing path, if the signal is a laborsaving signal, the controller controls the front electronic derailleur and the rear electronic derailleur to move the chain from one of the rear chain rings to another one of the rear chain rings along a laborsaving path of the gear-ratio table for decreasing the gear ratio and controls the front electronic derailleur to move the chain from one of the front chain rings to another one of the front chain rings at a second switch point of the laborsaving path, wherein the first switch point is different from the second switch point, and the front electronic derailleur and the rear electronic derailleur are started simultaneously at the first switch point or the second switch point, wherein at the first switch point, the front electronic derailleur and the rear electronic derailleur are started simultaneously, the front electronic derailleur moves the chain from one of the front chain rings to another one of the front chain rings within a first time and the rear electronic derailleur moves the chain from one of the rear chain rings to another one of the rear chain rings within a second time, wherein at the second switch point, the front electronic derailleur and the rear electronic derailleur are started simultaneously, the front electronic derailleur moves the chain from one of the front chain rings to another one of the front chain rings within a third time and the rear electronic derailleur moves the chain from one of the rear chain rings to another one of the rear chain rings within a fourth time, characterised in that the first time is longer than the second time, and the third time is shorter than the fourth time. triggering the controlling switch to generate a corresponding signal; and controlling the front electronic derailleur and the rear electronic derailleur by means of the controller according to the signal, if the signal is a speed-increasing signal, the controller controls the front electronic derailleur and the rear electronic derailleur to move the chain from one of the rear chain rings to another one of the rear chain rings along a speed-increasing path of the gear-ratio table for increasing the gear ratio and controls the front electronic derailleur to move the chain from one of the front chain rings to another one of the front chain rings at a first switch point of the speed-increasing path, if the signal is a laborsaving signal, the controller controls the front electronic derailleur and the rear electronic derailleur to move the chain from one of the rear chain rings to another one of the rear chain rings along a laborsaving path of the gear-ratio table for decreasing the gear ratio and controls the front electronic derailleur to move the chain from one of the front chain rings to another one of the front chain rings at a second switch point of the laborsaving path, wherein the first switch point is different from the second switch point, and the front electronic derailleur and the rear electronic derailleur are started simultaneously at the first switch point or the second switch point, wherein at the first switch point, the front electronic derailleur and the rear electronic derailleur are started simultaneously, the front electronic derailleur moves the chain from one of the front chain rings to another one of the front chain rings within a first time and the rear electronic derailleur moves the chain from one of the rear chain rings to another one of the rear chain rings within a second time, wherein at the second switch point, the front electronic derailleur and the rear electronic derailleur are started simultaneously, the front electronic derailleur moves the chain from one of the front chain rings to another one of the front chain rings within a third time and the rear electronic derailleur moves the chain from one of the rear chain rings to another one of the rear chain rings within a fourth time, characterised in that the first time is longer than the second time, and the third time is shorter than the fourth time.