A novel recessed gate graded AlGaN high-electron-mobility transistor (RGGA HEMT) for high-sensitivity terahertz (THz) detectors is reported, which exhibits significant potential for high-sensitivity THz detectors, and consequently. The simulation results indicate the exceptional field-effect factor of the proposed RGGA HEMT, which is largely attributed to the three-dimensional electron gas generated by the graded AlGaN barrier layer and the subsequent enhancement of channel conductance. The responsivity and noise equivalent power reach 58mA/W and 43pW/Hz respectively at 227GHz by utilizing a technical computer-aided design platform. As compared to conventional structure GaN HEMT experimental data, the current responsivity is improved by 2.64 times, and the NEP is reduced by 43.4%. The unprecedented improvement in detection performance renders the RGGA HEMT a highly promising approach for future THz real-time single-pixel imaging applications at room temperature. •The study innovatively introduces a recessed gate and three-dimensional electron gas into this type of detector for the first time.•This structure not only significantly improves the field-effect factor of the detectors but also reduces the channel resistance.•The method demonstrates a degree of universality, making it potentially extendable to transistor detectors composed of other material types.•It would be a promising approach to achieve terahertz imaging at room temperature and broad-spectrum detection of chemicals, owing to its outstanding responsivity and noise equivalent power (NEP).