Owing to their almost similarities in size, shape, and chemical reactivity, effectively distinguishing deuteroxide (D2O) in water (H2O) remains an ongoing challenge, and the examples of a D2O probe are still quite scarce. Herein, since H2O can decrease the lifetime of a singlet oxygen as a vital intermediate and an H/D exchange in the luminescence process of porphyrins, we systematically investigated the enhanced ultraviolet-visible (UV-vis), photoluminescence (PL), and electrochemiluminescence (ECL) of water-soluble tetrakis(carboxphenyl)porphyrin (TCPP) in D2O. The findings showed that these luminescent properties had been greatly enhanced with the increase of the D2O fraction in water. Consequently, we first developed the highly facile methods of detecting D2O in H2O by the UV-vis, PL, and ECL of TCPP, respectively. Impressively, the ECL analysis exhibited a great superiority with a lower detection limit of 0.29 nM. The work not only achieves the challenging task of distinguishing between H2O and D2O but also provides a unique strategy to enhance the luminescent performance of porphyrin.