In this paper, the progress in study of metastable beta titanium alloys with TWIP/TRIP effect (TRIP: transformation induced plasticity; TWIP: Twin induced plasticity, twin induced plasticity) is reviewed. The alloy-design ideas of TWIP/TRIP titanium alloy are described. The members in TWIP/TRIP titanium alloy family and their mechanical properties developed in recent years are introduced. The deformation products during plastical process and their correspongding formation mechanism are discussed. Finally the possible problems encountered in development of TWIP/TRIP Ti-materials are also presented.