Abstract: A new theory for Ti alloy plastic deformation is proposed. Experiment results showed that a new kind of tri-modal microstructure could be obtained using high temperature deformation strength-toughening. This microstructure strikingly raised low-cycle fatigue property, fatigue-creep interaction life, fracture toughness and service temperature of Ti alloy without reducing plasticity and thermal stability. The fundament of the new theory and strength-toughening mechanism bare also discussed. It was proved that high tem perature deformation strength-toughening was applicable not only in (α＋β) alloy, but also in α, near α, and near β Ti alloy.

Key words: Deformation, Strength-toughening, Three-morphology microstructure