This study used the pseudo-spinodal mechanism to obtain the ultrafine α phase for designing high-strength titanium alloy.Diffusion multiple experiments were designed to find the composition range of TM-xMo-yV alloy (TM: Ti-4.5Al-2Cr-2.5Nb-2Zr-1Sn) for obtaining ultrafine α phase.CALPHAD results confirm that when the alloy composition is located near the intersection of the α and β phase free energy curves,the alloy will undergo pseudo-spinodal transformation and obtain the ultrafine α phase.The designed TM-6Mo-3V alloy has a yield strength of 1411 MPa and an elongation of 6.5 ％.The strength of the alloy depends on the thickness,fraction of the α phase and the solid solution strengthening effect of the alloying elements.The deformation mechanism of the alloy is the dislocation slip of the α and β phases and the twin deformation of the α phase.The large number of α/β interfaces produced by the fine α phase is the main reason for limiting the ductility of the alloy.The use of the pseudo-spinodal mechanism combined with diffusion multiple experiments and CALPHAD is an effective method fordesigning high-strength titanium alloys.