The invention discloses a preparation method of a sodium carboxymethylcellulose thickening rheological agent for dry powder putty. With fibril as a raw material, the preparation method comprises the following four procedures: (A) pretreatment: grinding fibril, and preparing an alkalizer and a chloroacetic acid ethanol water solution; (B) alkalization: adding flocculent fibril into a kneading reactor, spraying the alkalizer to carry out alkalization, and spraying the chloroacetic acid ethanol water solution and acidy substances to react; (C) etherification: conveying the mixture to an etherification reactor, and carrying out etherification reactor; and (D) aftertreatment: drying, grinding, mixing, sieving, receiving and packaging products, so as to obtain a finished product. The sodium carboxymethylcellulose thickening rheological agent prepared by virtue of the preparation method is high in dissolving speed, and the viscosity, the consistency coefficient and the liquidity index are very applicable to the dry powder putty, so that the dry powder putty is light and rapid, is not sticky and greasy and does not sag in the scraping process, the scraping performance is effectively improved, the scraping efficiency is improved, and the labor intensity of workers is reduced.