Abstract: Disclosed are a modulated terahertz (THz) signal deflector and a preparation method thereof. The modulated THz signal deflector includes: a first transparent substrate and a second transparent substrate that are oppositely disposed, a liquid crystal layer, a transparent electrode layer, and a photo-alignment layer, wherein the photo-alignment layer has a control graph in which a molecule director is periodically and gradiently distributed along a specific direction, and the control graph is configured to control a liquid crystal molecule director in the liquid crystal layer to be periodically and gradiently distributed along a specific direction to form a blazed-grating phase distribution based on a geometric phase, and deflect an incident circularly polarized THz signal to a specific angle. The deflector provided in the present disclosure can deflect a THz signal to a specific angle, and can switch signal deflection and non-deflection functions by powering up a transparent electrode.