The invention discloses a fiber bending mode eliminating device and method; a multi-mode fiber is wound with an inner winding tool and an outer winding tool by means of double-curvature winding, so that the multi-mode fiber forms a small-radius winding portion wound on the inner winding tool and a large-radius winding portion wound on the outer winding tool. The multi-mode fiber is used as a transmission medium and is pre-wound according to two different radiuses, a higher-mode component coupled into the fiber is attenuated effectively with the small-radius winding portion, bending transmission mode possibly excited in previous step is eliminated with the large-radius winding portion, the inhibition on higher mode by the multi-mode fiber is achieved, output optical intensity is stable, an optical signal with mode eliminated outputs optical power that is kept constant during fiber moving, and using additional other detectors to assist in measuring position and other reference information during measurement of a scintillator position-sensitive nuclear detector is not required accordingly.