The invention discloses silk fiber used for a non-woven fabric and a preparation method of the silk fiber, and belongs to the technical field of nonwoven fabric materials. Pure natural mulberry silk is adopted, subjected to water-bath treatment by using a lithium bromide solution, then washed, and quickly dried, the stress in the silk is quickly changed, and modified silk with a certain degree ofbending is prepared. Compared with raw silk fiber, the bending degree of the modified silk fiber is greatly improved, strength is not significantly reduced, and the problems that through coating, blending, sericin bonding and other methods, the strength of cloth is improved unilaterally and the cloth is air permeable, moisture permeable and poor in softness can be solved. The modified silk fiber is excellent in performance, mild and free of stimulation, no other materials are introduced, the good performance of fibroin fiber can be give full play to and can serve as raw materials of a pure silk nonwoven fabric, the entanglement rate of silk in a spunlace silk nonwoven fabric is improved, the friction force in unit area is improved, and thus the strength of pure silk nonwoven fabric products is effectively improved.