Superplasticity of TiB_w /TA15 composite sheet under the conditions of 900–960℃ and 5×10^–4~10^–2 s^–1 was studied. The results showed the flow stress of TiB_w /TA15 composite decreases with the deformation temperature increasing and strain rate decreasing, and the strain softening characteristics are significant under the condition of low temperature and high strain. The maximum elongation obtained at 940℃ and 5×10^–3s^–1 was 439%. A constitutive equation based on the Zener–Hollomn parameter and Arrhenius equation was ε·=3.55×10⁸ [sinh（2.0×10^–2 σ）]^1.99 × exp（–6.381×10⁵ /RT） for TiB_w /TA15 composite，and the deformation energy Q=638.1kJ/mol. The superplastic deformation structure of composite materials is closely related to the tensile temperature and strain rate. The high temperature and low strain rate are beneficial to the dynamic recrystallization of the matrix α phase and the healing of the whiskers and the holes in the matrix. The change of grain size contributes more to superplasticity than the effect of voids on superplastic elongation. The low temperature and high strain rate are beneficial to the holes healing at the end of the interface between reinforced phase and matrix. Dynamic recrystallization plays a key role in superplasticity of composites.