The invention discloses a broadband-adjustable terahertz wave plate component which comprises two quartz substrates, metal wire gratings are arranged inside the quartz substrates, the metal wire gratings on two sides are parallel to each other, and the two quartz substrates form a liquid crystal box through frame glue. The liquid crystal box comprises an optical control orientation layer and a liquid crystal material. Liquid crystal is an electric control large birefringence liquid material. The optical control orientation layer and the liquid crystal material of the liquid crystal box achieve parallel orientation of the liquid crystal through an optical control orientation method, the orientation direction of the optical control orientation layer and the direction of the metal wire gratings form a 45-degree angle, and the liquid crystal box can achieve an adjustable one quarter or a half wave plate in a terahertz frequency range. The broadband-adjustable terahertz wave plate has the advantages of being wide in frequency range, self-polarization, high in transmittance, large in modulation quantity, fast in response and the like. In addition, the manufacture cost is low, efficiency is high, the broadband-adjustable terahertz wave plate can be produced in massive mode, and the application prospects are wide.