The invention belongs to the technical field of a detector, and specifically relates to a device used for terahertz wave detection and a preparation method therefor. By taking aluminum-gallium-nitride/gallium-nitride high-electron-mobility field effect transistor (HEMT) as a basic structure, an aluminum-gallium-nitride/gallium-nitride layer is prepared through substrate design and an epitaxial method; and next, an active region table surface, gate dielectric, an ohmic contact window and an electrode are prepared, wherein the two-dimensional electron gas in the obtained field effect transistor is relatively high in electron concentration and mobility, a wave spectrum detection apparatus with high-speed, high-sensitivity and high signal to noise ratio detection can be realized on THz at a room temperature, and terahertz wave detection is realized finally.