Due to the particularity of its material, corrugated cardboard will be affected by environmental humidity during transportation. Therefore, the model of plateau stress in standard environment is studied firstly, and then the humidity factor is introduced to modify the model. The method of experiment and theoretical modeling is used to establish the theoretical model of the longitudinal compression plateau stress based on the environmental humidity. Through experimental methods, the ultimate stress of corrugated paper is discussed with the environmental humidity, and its characteristic curve with environmental humidity is established. Then it is introduced into the theoretical model of plateau stress under standard environment, and the theoretical model of plateau stress under arbitrary environmental humidity is established. Compared with the corrugated cardboard plateau stress established without considering the humidity, the theoretical model established with the humidity considered has a better consistency with the tested results, which verifies the accuracy of the model. The established theoretical model under any humidity has a good predictive effect on the plateau stress, and at the same time has a great guiding effect on the selection of corrugated cardboard and packaging design.