Precise measurement and visualization of trans-/supercritical jet processes are of great significance for the control of power engines, chemical reaction and industrial processes. The quantitative measurement of transcritical jet under the influence of high pressure effect and transient effect is the key issues in such analysis. In this study, an improved phase-shifting interferometer system with high temporal and spatial resolution (0.001 s, 3.45 μm) has been realized by pixelated-array masked method to investigate characteristics in trans/supercritical jet processes. The transient density field and boundary structure of the phase-transition interface during four jet processes under sub/trans/supercritical conditions were quantitatively measured, which is different from those under subcritical conditions. The results show that the characteristic of subcritical jet is phenomenon of fragmentation and atomization within the experimental cell due to the presence of interfacial tension and strong density pulsations. The atomization is suppressed by high pressure effect in supercritical jet. Instead, Instead, single-phase mixing occurs due to the absence of surface tension. The dense core is found gradually dissolved during diffusion process of the jet flow. The transition from liquid-like to gas-like status of fluid occurs when the injection fluid goes cross the pseudo-critical line, and the jet surface has a large density gradient (in the current test range, | ρ|max = 8 × 105 kg/m4) due to temperature rise and pseudo-boiling expansion.