The invention discloses a double-step floating burr removing device of crankshafts. The device comprises a speed reduction motor, a coupler, a main drive shaft, an auxiliary transmission shaft, a synchronous belt, a synchronous pulley, flexible cutter bars, brushes and the like, wherein an input end of the main drive shaft is connected to an output shaft of the speed reduction motor, one flexible cutter bar is arranged at an output end of the main drive shaft, an input end of the auxiliary transmission shaft is connected to the input end of the main drive shaft through the synchronous pulley and the synchronous belt, and the other flexible cutter bar is arranged at an output end of the auxiliary transmission shaft. Flexible chucks used for fixedly installing the brushes are arranged in ends of the flexible cutter bars. The device has the effects that the overall structure is simple; the main drive shaft and the auxiliary transmission shaft are connected through the synchronous pulley and the synchronous belt, the rotation driving force from the motor is divided into two parts so as to realize simultaneous feeding machining, and the machining efficiency is improved; and the flexible cutter bars are matched with a robot to remove burrs, rigid contact between cutters and work-pieces is prevented, and the service life of equipment is prolonged. The invention further provides a machining method of the device. The method has the advantages that the machining steps are simplified, and the qualification rate of products is high.