HTPB composite solid propellant containing slant internal cracks under uniaxial tensile load were measured by using of material testing device WDN-10KN, with the tensile rate of 2 mm·min^-1.The whole progress of Crack propagation was recorded by camera. Curves of the Loading-Displacement, crack initiation angle and fracture loading were obtained. By comparison with series fracture criteria including T-Criterion, S-Criterion, σ_θ-Criterion, the crack initiation angle of solid propellant obtained is in approximately agreement to that from T-Criterion, showing that the T-Criterion can be used as a theory prediction to the crack initiation angle of the composite solid propellant.