Double row angular contact ball bearing mounted on the input shaft of the vehicle automatic transmission has the separable inner ring. Therefore, the plastic locking ring is clamped to prevent separation during bearing transfer. In this study the coefficient of linear expansion of low density polyethylene(LDPE), which is used as a material of plastic locking ring, was measured and the contraction, expansion and clamping force of plastic locking ring according to temperature change were calculated by finite element analysis(FEA). Based on this, we proposed a design method of locking ring that can maintain the clamping force even at -20℃.