The utility model relates to a fixing device with have fixing device's motor feedback system. Be used for the axle coaxial fixedly to the epaxial fixing device of rotary encoder with have fixing device's motor feedback system. For can be coaxial and to fasten rotary encoder with the axle each other epaxial with aiming at, according to the utility model provides a fixing device for inciting somebody to action the axle is coaxial fixed with the rotary encoder axle, fixing device has: the axle sleeve, its arrange between axle and the rotary encoder axle and the compensating shaft between the diameter poor, press from both sides tight unit, it aims at the rotary encoder axle with the axle sleeve and fasten axle sleeve and rotary encoder axle epaxial, and wherein, double -layered tight unit has: axial alignment device, it is used for making tight unit of clamp and axle sleeve to aim at the rotary encoder axle, and, radial fixer, it is used for fixed axle sleeve, rotary encoder axle and axle.