The mechanical properties of single-chamber dual thrust grain were studied especially on the interface of the two propellant grains. The tensile strength and the elongation of propellants with different compositions prepared by different technologies were measured at 20 ℃,50 ℃,and -40 ℃. The surface appearance and the element distribution on the failure surface were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS). Results show that the interfacial mechanical properties are close to that of cast propellant,and the mechanical properties of the interface has almost no effect on the whole mechanical properties of propellant. Al₂O₃ powders,one of the components in the propellant,are found to cumulate around the interface.