Abstract: The effects of cold deformation and aging treatment on the microstructure and properties of Ti-15Mo-3Al-2.7Nb-0.2Si titanium alloy were investigated by optical microscopy(OM),X-ray diffractometer(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electronic tensile testing machine. The results show that no phase transition occurs during the cold deformation of the alloy.With the increase of cold deformation,the lattice of the alloy gradually rotates toward the direction of<011>. Ageing after cold deformation of the alloy precipitates uniformly distributed fine needle-like α-phase,which has a very good co-grid relationship with the β-matrix,which contributes to the performance of the alloy. Cold-deformation-aged alloys are mainly strengthened by aging precipitation and supplemented by deformation strengthening. Cold deformation can promote aging precipitation,and the larger the cold deformation,the more obvious the ageing precipitation strengthening effect. The ultimate tensile strength of the alloy treated with 60% cold deformation aging reaches 1786 MPa.