Triboelectric nanogenerator (TENG)’s use is constrained by their surface charge density and alternating current output. This study therefore proposes a coupling output method combining charge excitation and phase shift to realize an almost constant high-performance direct-current (DC) and DC-TENG is designed to harvest the energy of flowing water. The output characteristic of the DC-TENG with or without charge excitation is thoroughly investigated in the experiment. The impact on the effectiveness of phases (P) and groups (G) is further proven by comparing and quantifying the current wave. The operation capability in a water environment is further demonstrated by the transmitted charge's attenuation of roughly 10.84% after the environment's humidity is increased to 90% RH. According to the findings of the investigation, DC-TENG with 3P4G can reach almost constant DC with the root mean square value of 29.1 μA and the crest factor of 1.23. And the 220 μF capacitor can be charged to 5 V within 63 s and the peak output power of 9.18 mW is obtained. Finally, an experimental platform is established to simulate the water environment and the thermography is steadily powered. This scheme has reference significance to realize high-performance DC output in the water environment.