The main reason for the high strength in near-β titanium alloys is the ultrafine precipitation of the acicular secondary α phase in the β matrix.The purpose of this study is to use the pseudo-spinodal mechanism to obtain the ultrafine α phase for the design of a new high-strength near-β titanium alloy.Thermodynamic calculations and TC21-(TC21+ 15Mo) diffusion couple composition gra-dient experiments were used to demonstrate that TC21 +3Mo alloy can undergo a pseudo-spinodal decomposition to obtain the ultrafine α phase,resulting in a high-strength alloy.By adjusting the heat treatment process to obtain a bimodal microstructure,the alloy exhibits a good balance between ultimate tensile strength (1351 MPa) and plasticity(8.5％ strain).Thus,it was demonstrated that the pseudo-spinodal mechanism combined with a high-throughput diffusion couple technique is an effective method for designing high-strength titanium alloys.