The invention discloses a THz (Terahertz) wave modulator. The THz wave modulator comprises a semiconductor substrate (1), MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) arrays (2), metamaterial resonance unit arrays (3), a first metal plate (4) and a second metal plate (5), wherein THz wave can permeate the semiconductor substrate (1), the MOSFET arrays (2) are distributed on the semiconductor substrate (1) according to a certain period, the metamaterial resonance unit arrays (3) are prepared on the MOSFET arrays (2), the first metal plate (4) is connected with a source electrode and a drain electrode of each MOSFET, and the second metal plate (5) is connected with a grid electrode of each MOSFET. According to the THz wave modulator disclosed by the invention, the working voltage of the MOSFET is very low, and thus the THz wave modulator prepared by the MOSFET can work under low voltage; and the switching time of the MOSFET is extremely short, the magnitude order of the switching time is 10-100ns, and thus the modulating rate of the THz wave modulator prepared by the MOSFET is larger than 10MHz.