High-color-fastness plant yarn dyeing method based on first color fixing and then dyeing

The invention discloses a high-color-fastness plant yarn dyeing method based on first color fixing and then dyeing. The method comprises the following steps: (1) performing health-preserving treatment on fibers by using a health-preserving auxiliary agent; (2) after the curing treatment is completed, opening and carding the fibers, carrying out color fixation on the carded net fibers by adopting nano silicon dioxide sol, then drawing, and drying fiber strips by virtue of a drying device; (3) roving and spinning the fiber strips to obtain nano silicon dioxide modified yarns; and (4) carrying out plant dyeing on the nano silicon dioxide modified yarn to obtain the plant-dyed yarn. According to the invention, the water-soluble health-preserving auxiliary agent is added before carding for health preserving, and the nano silicon dioxide sol is sprayed after carding, so that the problem of difficulty in carding caused by overlarge friction force of fibers before carding is avoided, and the friction coefficient of t