Abstract: To understand deeply the active characters of groups in the binder of Hydroxyl terminated polybutadiene (HTPB) propellants，in which the groups react easily with other materials in the store period，and to find a method to decrease the aging of propellants and extend the store life of rocket motor，the chemical reactiveness of the functional groups in tolylene diisocyanate (TDI)/HTPB binder was studied by means of quantum chemical calculations and IR spectrum analysis. The effect of the active group aging on the mechanical property of HTPB propellant was also investigated. The quantum chemical calculations show that the active groups in the dhesive matrix are C=C bonds and urethane groups. IR spectrum analysis confirms that the aging the binder mainly concerns the oxidation of C=C bonds，which contributes to the destruction of the adhesive matrix and then results in decreasing the mechanical properties of HTPB propellant during the storing.