Studied the hygroscopic properties of a molded combustible cartridge case by weighing method. Investigated residue formation of cylinder materials with different water content by nitrogen-bomb tests. The results show that the higher the relative humidity, the greater the equilibrium moisture content of the inside-wall material. When the relative humidity was about 90%, its absorption rate was about 5.4%. Compared with its outside wall, the inner parts have much stronger moisture absorption properties. The combustion remains grew in quantity generally with the increase of moisture content.