For the loading features of propellant, the mechanical properties were studied by brazilian test. Theories of Hertz elastic contact and elastic mechanics plane stress were applied to analyze the stress distribution law, and the formula was obtained to calculate tensile strength for propellant from Griffith strength criteria. Results show that the initial crack forms at the center region of propellant and propagates along the loading direction, which proves that the Brazilian test is suitable for measuring tensile strength of propellant. The tensile strength of propellant is determined by the load when the splitting happens and the contact width between propellant and indenter. When the storage time extends from 39 years to 47 years, the tensile strength of propellant changes from 13.11 MPa to 12.58 MPa, decreasing by 4%.