The invention relates to a method for preparing carboxymethyl maca polysaccharide. The method comprises the following steps of: extracting maca polysaccharide from maca dry powder by taking water and ethanol as media; reacting the maca polysaccharide with chloroacetic acid and properly excessive sodium hydroxide in an isopropanol medium; performing a substitution reaction on hydroxide radicals in the polysaccharide; and removing proteins of the mixture and dialyzing the mixture to obtain high water-solubility carboxymethyl maca polysaccharide. Compared with the prior art, the preparation method has the advantages of simplicity, convenient operation, high water solubility of the obtained carboxymethyl maca polysaccharide, simple raw materials, low cost, high reaction speed, easy control, easy separation of the product and high purity of the obtained carboxymethyl maca polysacchatide; and the high water-solubility carboxymethyl maca polysaccharide prepared by the invention has the substituting degree of 0.618.