The stress corrosion behavior of cast Ti-6Al-4V alloy, as an important engineering material of key structural components for deep-sea applications, in actual deep-sea conditions still remains unclear. In this study, the effect of hydrostatic pressure on the stress corrosion sensitivity and electrochemical behavior of the cast and forged Ti-6Al-4V alloys was comparatively studied by means of slow strain rate tensile testing and electrochemical testing techniques, scanning electron microscopy with electron backscatter diffraction (EBSD), etc. The results indicate that under the combined influence of high hydrostatic pressure and tensile stress, the transition of passivation films of both cast and forged Ti-alloys could occur from a dense structure gradually to a porous structure, thereby reducing their protectiveness. The coarse β-phase grain boundaries and defects in the cast Ti-alloy act as sites of weakness in the passivation film, which could significantly lower the compactness and corrosion resistance of the passivation film for the cast Ti-alloy. However, this effect was not observed in the forged Ti-alloy. The stress corrosion sensitivity of both types of Ti-6Al-4V alloys increases with hydrostatic pressure. In contrast, by the same hydrostatic pressure, the stress corrosion sensitivity of the cast Ti-6Al-4V alloy is higher than that of the forged Ti-6Al-4V alloy. Under high hydrostatic pressure, brittle fracture occurs for the cast Ti-6Al-4V alloy, and while ductile-brittle fracture for the forged Ti-6Al-4V alloy. Under high hydrostatic pressure, the applied tensile stress can induce dislocation motion, leading to stress concentration at the original β-phasegrain boundaries of the cast Ti-6Al-4V alloy. In fact, the existence of segregation defects can lead to the preferential damage of the passive film at those sites, and the cracks at the dendrites can initiate and propagate along the α/β phase interface in between the layers, and thus, the stress corrosion sensitivity is high. In contrast, the forged Ti-6Al-4V exhibits an equiaxed structure with a relatively dense passivation film, uniform deformation, and a strong ability of equiaxed crystals to resist crack propagation, thereby exhibiting relatively lower sensitivity to stress corrosion cracking.