The invention discloses a thickening agent for printing, which comprises the following components in parts by weight: 10-15 parts of etherified guar gum, 60-70 parts of sodium alginate, 30-50 parts of sodium carboxymethylcellulose, 20-30 parts of carboxymethyl starch, 12-20 parts of polyacrylic acid thickening agent blending stock, 10-20 parts of bentonites and 200-400 parts of water. The preparation method of the thickening agent comprises the following steps of: adding sodium alginate and sodium carboxymethylcellulose powder to water, and mechanically stirring till a solution is transparent and clear without a block; then adding the etherified guar gum, the carboxymethyl starch, the polyacrylic acid thickening agent blending stock and the bentonite, uniformly stirring, and standing to bulk the mixed solution so as to obtain the printing thickening agent. In the preparation process, with the bulking of the paste material, the sodium carboxymethylcellulose forms three-dimensional net structure among macromolecules of paste material or at the joints of molecular chain segments because of intermolecular attraction; moreover, besides a macromolecular chain hydration layer, a large amount of water is wrapped to form a gel state, so as to generate very high structural viscocity; therefore, a printing fabric has a clear outline.