The hexagonal closest packed (hcp) to face‐centered cube (fcc) phase transformation of Ti(Pt) alloy with phase transformation pressure of ≈36.8 GPa at 0 K is found using the first‐principle method. The relatively low phase transformation pressure of hcp to fcc structure for Ti(Pt) alloy may be caused by the foregoing tetragonal isostructural transition of fcc Ti(Pt) alloy at ≈32 GPa. Accompanied with the tetragonal isostructural transition, the unit‐cell parameters (a, c) and volume of fcc Ti(Pt) alloy are discontinuous. The axial ratio (c/a) changes from ≈0.471 to ≈0.338; a axis has anomalously negative compressibility, c axis has positive compressibility. Anomalous elastic properties between 32 and 40 GPa, such as the extremely irregular elastic stability factor F and elastic anisotropy index AU, indicate the weak mechanical stability of fcc Ti(Pt) alloy in the phase transformation region. The total density of states, Mulliken population analysis, and difference of charge density indicate that the Pt–Ti interatomic interactions weaken with increasing pressure.