The invention discloses a preparation method of self-crosslinked AM/AA grafted-esterified hydroxypropylated cassava starch. The preparation method comprises the steps of enabling cassava starch serving as the main raw material to react with epoxypropane in absolute ethyl alcohol under the action of sodium hydroxide serving as a catalyst to obtain hydroxypropylated cassava starch; then, synthesizing esterified hydroxypropylated cassava starch by taking benzoyl chloride as an esterifying agent; and next, carrying out graft polymerization reaction on the esterified hydroxypropylated cassava starch by taking a mixture obtained by mixing trimethylamine neutralized acrylic acid, acrylamide and N, N'-methylenebisacrylamide as a mixed monomer and a mixture of sodium bisulfate and ammonium persulfate as a mixed initiator to synthesize crosslinked AM/AA grafted-esterified hydroxypropylated cassava starch. The self-crosslinked AM/AA grafted-esterified hydroxypropylated cassava starch has the hydroxypropyl substitution degree of 0.12-0.14, the esterification substitution degree of 0.08-0.11, the grafting efficiency of 79.5% and the monomer conversion rate of 96.5%. Various functional groups are introduced to the self-crosslinked AM/AA grafted-esterified hydroxypropylated cassava starch after the self-crosslinked AM/AA grafted-esterified hydroxypropylated cassava starch is modified through a plurality of steps; and the self-crosslinked AM/AA grafted-esterified hydroxypropylated cassava starch has a complex stereoscopic net-like structure, is combined with heavy metal ions and some insoluble matters in water through adsorption and is applied to the aspects of heavy metal adsorption, environment friendliness, functional materials and the like.