Abstract: This study evaluates the capability of three high-resolution reanalysis datasets (GLORYS12V1, HYCOM, and BRAN2020) in depicting the three-dimensional structure of a complete intrathermocline eddy (ITE) captured by a buoy in the tropical southeastern Indian Ocean. The results show that all three datasets reasonably reproduce the surface anticyclonic structure. For subsurface temperature and salinity simulations, only GLORYS12V1 successfully reproduces the ITE’s typical “lens-like” structure and high-salinity core features. However, none of the datasets capture the strong northward current with a peak velocity of 60 cm/s at 100 m depth, revealing biases in simulating subsurface flow fields. Further analysis based on GLORYS12V1 reveals that this eddy exhibits characteristics of high-order baroclinic modes and continuously receives a supply of equatorial water masses via geostrophic currents during its propagation, providing a key maintenance mechanism for its exceptionally long lifespan.