A package material integrating humidity constant property and buffer function together was designed based on self-made spongy polyurethane-poly(acrylic acid-acrylamide) (PU-PAA/AM) humidity constant intelligent material. The method and formula to realize constant humidity in packaging internal environment through control of pre-absorption time was put forward according to the relation between moisture content and pre-adsorption time, and equilibrium moisture content and relative humidity. The packaging material integrates buffer function and humidity constant property together, so it is can be widely used in weapons storage packaging and transportation.