The average molecular weight of the raw material polyvinyl alcohol used for the polyvinyl alcohol fiber is 60,000-150,000, the thermal decomposition temperature is 200-220°C, and the melting point is 225-230°C. Polyvinyl alcohol fibers can be obtained by wet spinning and dry spinning. The polyvinyl alcohol fiber after the heat treatment can be obtained by acetalizing the polyvinyl alcohol fiber. The acetalization process is to wash the tow with water to remove Glauber's salt (sodium sulfate), then pass through the hydroformylation solution (composed of formaldehyde as the formaldehyde agent, diluent water, catalyst sulfuric acid, and anti-swelling agent sodium sulfate), and then wash with water. the process of. The tow can also be cut into short fibers, transported to a post-processing machine by air flow, and acetalized on a stainless steel wire. In order to improve the fiber properties, the polyvinyl alcohol solution (concentration of 16%) containing the cross-linking agent boric acid can be wet-spun, and the obtained primary fibers are coagulated in an alkaline coagulation bath, neutralized, washed with water and multi-stage high-stretching. And heat treatment, the filament with the strength of 106-115cN/dtex can be obtained.