The invention relates to an infrared detector and a preparation method thereof. The infrared detector comprises a substrate, a dielectric layer, an electrode layer and a thermosensitive layer, wherein the dielectric layer, the electrode layer and the thermosensitive layer are located on the substrate, the electrode layer is located between the dielectric layer and the thermosensitive layer, the dielectric layer is located on the side, which is close to the substrate, of the electrode layer, and the electrode layer is in contact with the thermosensitive layer; the infrared detector comprises a plurality of infrared detector pixels arranged in a matrix, each infrared detector pixel comprises an absorption plate structure, at least two micro-bridge columns and at least two beam structures, and the absorption plate structures are connected to the corresponding micro-bridge columns through the corresponding beam structures; the thermosensitive layer covers the area where the absorption plate structure and the beam structure are located; the material for forming the thermosensitive layer comprises one or more of amorphous silicon, amorphous carbon, amorphous germanium or amorphous silicon germanium; and the material for forming the electrode layer at least includes titanium. According to the technical scheme, the thermal response time of the infrared detector is shortened, and the infrared response rate of the infrared detector is improved.