The invention discloses a preparation method and product of sunscreen woven bag flat yarn and woven bag. The flat yarn is made of polypropylene, antiaging agent, coupling agent, antioxidant, nano calcium carbonate, polyoxymethylene, linear low density polyethylene , polyethylene wax, ethylene-methyl acrylate copolymer, tributyl citrate, turpentine, ultraviolet absorber and additives are stirred evenly, then plasticized into a molten state at a temperature of 230°C to 240°C, and extruded into a film. It is obtained by cooling, cutting embryo silk, and stretching it into flat yarn. The obtained flat yarn is woven into a sunscreen woven bag. The prepared sunscreen woven bag flat yarn has a good breaking strength retention rate after being exposed to the outdoor atmosphere for one year. and elongation retention at break, and good sun protection performance. The performance and service life of the woven bag after using the flat yarn are improved, and the toughness and tensile strength of the original flat yarn are maintained.