The invention discloses a method for preparing a crystalline-state nano structure based on a femtosecond laser-induced amorphous GemSbnTek thin film, and belongs to the technical field of femtosecondlaser application. The size of a single incident femtosecond laser pulse focused light spot is controlled within a certain energy range, so that control over processing and the size of the GemSbnTek crystalline-state nano particle is realized, when the focused light spot is relatively large, the nano particle with a relatively large diameter can be obtained, and when the size of the focused lightspot is reduced, the diameter of the nano particle can be reduced. The laser frequency and the movement speed of a translation table are integrally controlled so that large-area efficient preparationof the high-consistency and uniform crystalline-state nano particle can be further realized. According to the method, compared with an existing nano structure processing method, the processing precision and processing efficiency of the nano structure are effectively improved, controllable preparation of the single nano structure and the composite nano structure is realized, meanwhile, the change of the crystalline nature of the super-fast phase change material GemSbnTek nano structure is realized, and the method has critical application value in the aspects such as information storage, metamaterial, nanometer antennas and light control.