In the process of dyeing and finishing, the warp direction of the fabric is under tension, the buckling wave height of the warp direction is reduced, and the phenomenon of elongation occurs. When the hydrophilic fiber fabric is soaked in water and soaked, the fiber swells and the diameter of the warp and weft increases, which increases the buckling wave height of the warp yarn and shortens the length of the fabric, resulting in shrinkage. The percentage of shortened length to the original length is called shrinkage. Mechanical preshrinking is to spray steam or spray the fabric to wet, and then apply warp mechanical squeezing to increase the buckling wave height, and then dry it loosely. The shrinkage rate of the pre-shrunk cotton fabric can be reduced to less than 1%, and the softness of the fabric will also be improved due to the mutual extrusion and rubbing between the fibers and yarns. The wool fabric can be treated with relaxation and pre-shrinkage. After the fabric is immersed in warm water or sprayed with steam, it is slowly dried in a relaxed state to shrink the warp and weft directions of the fabric.