The thermal decomposition behaviors of single-base propellants stored with different humidity were studied by using microcalorimetry with sealed and open glass test-tube. The experimental results show that under the same humidity condition,the temperature of initial accelerating thermal decomposition of single-base propellant under the sealed condition,Ｔ_０,is larger than that under the open condition. The temperature corresponding to maximum decomposition rate of single-base propellant under the sealed condition,Ｔ_Ｐ２,reduces obviously with humidity increasing,but that under the open condition does not. The process and reaction accelerating extent of the decomposition reaction of single-base propellant under the sealed condition are greater than those under the open condition.