This article studies the phase transformation of the metastable beta-Ti-Al-Mo-V-Cr-Zr alloy (Ti-1300) to disclose the morphological reason for its high strength and high fracture toughness. It has been found that its ultrahigh strength (ultimate tensile strength exceeds 1400 MPa) owes mainly to the spheroidization of the alpha-phase, while the high fracture toughness (exceeds 81 MPa.m(1/2)) to the special lath-shaped alpha-particles. Compared to the needle-shaped second alpha-articles, the coarser lath-shaped ones remove the stress concentration at the lath tips and consequently benefit improvement of fracture toughness. The article also describes shape evolution of the alpha-particles during aging thermodynamically and kinetically, and suggests an optimized aging processing to achieve an ideal balance between high strength and high toughness for this alloy.