Twenty simulant bones (polymethacrylate cylinders) were used in this experiment.The mid-shaft of each simulant bone was fixed with 316L stainless steel plate.Four of the 20 were served as control(no washer group) and the other 16 as experimental group(washer group).In the latter,different numbers and thickness of UHMWPE washers were inserted in between the screw-hole walls and the screws.The longitudinal loading test was performed immediately,and at 4,8,12and16 weeks after plate fixation,respectively.The strain of the surface between 2 screw holes in the plate and on the mid-shaft of the simulant bones apposite the plate was measured so as to calculate the stress shielding rate of plate on bone.The results demonstrate that the stress shielding rate of plate on bone would gradually decrease in the washer group and keep constant in no washer group after fixation.Ten weeks later,there was significant difference of the stress shielding rate between the two groups.The resutls also show that if the thickness of the washers remain unchanged,the greater the number,the more obvious the reduction of the stress shielding rate at the later stage.It is suggested that the stress shielding rate of the plate on bone in the washer group is closely related to the number of washers.