The invention provides a terahertz modulator based on low-dimension electron plasma waves, a manufacturing method thereof and a high-speed modulation method. The terahertz modulator comprises a plasmon and a resonant cavity. The resonance absorption mechanism is caused by electronic collective oscillation (plasma waves, namely Plasmon). In order to increase the coupling strength of the plasma waves and the plasmon, a GaN/AlGaN high-electronic-mobility transistor structure with a raster grid is integrated in a terahertz Fabry-Perot resonant cavity, plasmon polariton is formed through strong coupling of the plasmon and the resonant cavity mode. By means of the strong coupling effect, the transmission coefficient of the resonant cavity mode is the maximum at the resonance point, resonance conditions of the plasmon and the resonant cavity mode are adjusted and controlled by changing the raster pressure, and efficient and high-speed modulation for terahertz waves is achieved. The working principle and the achieving technology of the device are introduced in detail, and a good solution is provided for relevant applications.