The invention relates to a preparation method of a micro-bridge structured infrared detector, and a micro-bridge structure. The method comprises the steps that: a metal reflective layer and a sacrificial layer are sequentially deposited on an infrared detector readout circuit substrate; PI holes are etched on the sacrificial layer, wherein the PI holes are positioned at an out-leading electrode of the readout circuit; a deposition support layer, a thermo-sensitive layer and a protective layer are sequentially deposited on the sacrificial layer; through holes are prepared in the PI holes, and a contact hole is prepared on the protective layer; electrode layer metal is deposited on the protective layer, and U-shaped metals with bridge pier structures are filled in the PI holes and the through holes; and U-shaped metal structures are formed through photolithography and etching; photolithography and etching is carried out upon the electrode layer metal; a passivation layer is deposited on the surface of the device, and the passivation layer is subjected to photolithography and etching, such that a passivation layer pattern is formed; and sacrificial layer releasing is carried out, such that the micro-bridge structure is formed. According to the invention, a U-shape filling method is adopted, and Al is adopted as a filling material. Therefore, sputtering and depositing are easy, and etching is convenient. The heat insulation property of the detector is better than that of a copper filling process, and a CMP step is not needed.