Used in the manufacture of polyvinyl acetal, gasoline-resistant pipes and vinylon, fabric treatment agents, emulsifiers, paper coatings, adhesives, etc. The invention relates to a water-soluble polyvinyl alcohol fiber and a preparation method thereof. The invention is characterized in that 100 parts of polyvinyl alcohol with a degree of polymerization of 500-2000 and a degree of alcoholysis of 75-99 mol% and 200-400 parts of a mixed solvent of dimethyl sulfoxide/water (90-70:10-30) are added to a stainless steel dissolving kettle, dissolved for 3-4 hours at a temperature of 80-120°C and a pressure of -0.01-0.08 MPa under stirring, and a spinning solution is prepared. The water-soluble polyvinyl alcohol fiber is obtained through filtration, degassing, dry-wet spinning and post-treatment. The fiber has a water-soluble temperature of 10-90°C, a strength of ≥3.5 cN/dtex, a single fiber fineness of 1.5-10 dtex and an elongation at break of 15-30%. The filaments are processed into slivers, which can be blended with wool slivers, cotton slivers, hemp and chemical fibers to produce high-count yarns or hollow yarns, or cut into short fibers for various uses such as non-woven fabrics, embroidery base fabrics and papermaking. It has the following excellent properties: PVA is soluble in water, with solubility increasing with increasing water temperature. However, it is virtually insoluble in organic solvents. PVA solubility varies with the degree of alcoholysis and degree of polymerization. Partially alcoholyzed PVA and PVA with a low degree of polymerization dissolve very quickly, while completely alcoholyzed PVA and PVA with a high degree of polymerization dissolve more slowly. Generally, the degree of alcoholysis has a greater impact on PVA solubility than the degree of polymerization. The PVA dissolution process occurs in stages: affinity wetting, swelling, unlimited swelling, and dissolution. Film-forming PVA easily forms films, and its mechanical properties are excellent. The tensile strength of the film increases with increasing degree of polymerization and degree of alcoholysis. Adhesive PVA exhibits excellent adhesion to hydrophilic cellulose. Generally, higher degrees of polymerization and alcoholysis increase the bonding strength. Thermal stability: PVA powder gradually changes in appearance when heated to around 100°C. Partially alcoholyzed PVA begins to melt at around 190°C and decomposes at 200°C. Completely alcoholyzed PVA begins to melt at around 230°C and decomposes at 240°C. Thermal cracking experiments show that the lower the degree of polymerization, the faster the weight loss; the higher the degree of alcoholysis, the shorter the decomposition time. Medical PVA includes grades such as PVA05-88, PVA17-88, and PVA-124. The alcoholysis degrees of the first two grades are both (88±2) (m01)%, with average degrees of polymerization (n) ranging from 500-600 and 1700-1800, respectively. PVA-124 has an alcoholysis degree of 98-99 (m01)%, with an average degree of polymerization (n) ranging from 2400-2500. Developing new pharmaceutical excipients and promoting dosage form optimization are currently strategic tasks for Chinese traditional medicine development to align with international standards. PVA offers advantages such as ease of synthesis, safety, low toxicity, easy quality control, low price, and ease of use. Therefore, PVA is an excellent pharmaceutical excipient with potential for further development.