In order to obtain the changing status of mechanical properties of HTPB propellant under high-low temperature cyclic environment, the changing laws of mechanical properties of HTPB propellant were investigated by high-low temperature cyclic test (i. e. the test of gradually changing temperature environment) and uniaxial tensile test. The results of experiments show that maximum tensile strength and elongation at maximum tensile stress decrease with increase of high-low temperature cyclic cycles, and the changing laws of mechanical properties of HTPB propellant under high-low temperature cyclic environment are different from those under storage aging. At last, based on the grey theory, high-low temperature cyclic failure cycles of HTPB propellant under the experimental condition was predicted.