Starch, PVA and acrylic polymer are the main three sizes used in starching warp. PVA has the benefit of avoid permeation and film forming, but it is unfavorable to desizing process and causes pollution. Production of modified starch size and key technology for PVA substitution have the advantages of reducing the difficulty of desizing, wakening process conditions, shortening process time, and improving the first-class product rate of dyeing and printing.