Abstract-The ignition behavior of laminated propellants composed of ammonium perchlorate (AP) single crystal oxidizer and carboxyl terminated polybutadiene (CTPB) fuel-binder slab, has been studied by means of CO2laser under sub-atmospheric pressure. The ignition is initiated by the reaction of carbonaceous material on AP surface with AP decomposition products and ambient helium gas has appreciably preventive influence on propellant ignition, compared with Ar and N2 gases. These phenomena might be explained by a comprehensive ignition model.