Objective To analyze the changing characteristics of foamed polyethylene EPE cushion after a long time of product loading. Methods Two different load weights (-15. 3, 22. 2 kg) were set to simulate the weight of certain electronic product in this controlled study, with a preloading of 72 h, and the deformation of the internal buffer material after long time stacking compression was checked. Then the stress-strain curves, the maximum acceleration-static stress curves and cushion coefficient-maximum static stress curves under two different pre-loading weights were compared. Results Preloading could shorten the yield segments, decrease the property of energy-absorbing, and increase the minimal acceleration values and minimal cushion coefficient values. Conclusion Preloading could greatly weaken the cushioning performance of EPE buffer material. It is recommended that pre-conditioning should be done prior to the dynamic test for expanded materials, therefore it could better resemble the actual using condition.