A method for controlling back clearance of a motion transmission apparatus, is capable of controlling the generation, reduction and even elimination of a back clearance of a motion transmission apparatus to meet different needs. The motion transmission apparatus comprises: a first electric motor, a second electric motor, and a toothed member engaged with the first and second toothed drive members, when the toothed member needs to be precisely positioned, the back clearance between the second electric motor and the toothed member at different positions of the toothed member will be controlled according to the torque change, so as to consequently change a position offset of the second electric motor with respect to the first electric motor, when the toothed member doesn't need to be precisely positioned, the second electric motor shouldn't be controlled.