Abstract: For 3D braided CMC owing to interfacial fracture, it is remarkable that interfacial fracture mode mixing Ψ works on the material fracture toughness. Although the interfacial fracture mode mixing can hardly be determined because its expression involves an uncertain parameter-fracture length eigenvalue, the fracture mode mixing at the tip of crack Ψ_tip, which correlates with Ψ, can be decided uniquely. So the fracture toughness of 3D braided CMC material can be researched on interfacial cracks with Ψ_tip. By numerical simulation, this paper analyses the relation of the mixing Ψ_tip with the declining angle and interfacial thickness, further researches the influence of the 3D braided CMC's cracks path on the mixing Ψ_tip, and finds a way of fracture design of 3D braided CMC.