The invention discloses a preparation method of a sulfonic acid type aromatic block cation exchange resin. The preparation method comprises following steps: a chloromethylation reagent and a catalyst are added into a block polymer solution, and a precipitating agent is added dropwise so as to obtain a precipitate; after drying, an obtained chloromethylation block polymer and toluene are mixed, styrene, complex triphenyl phosphine, and a catalyst are added successively, stirring dissolving is carried out, nitrogen is introduced under vacuum conditions, heating is carried out, ascorbic acid is added, styrene is added, an obtained product is subjected to precipitation, filtering, washing, and drying so as to obtain a grafted product; concentrated sulfuric acid, acetic anhydride, and 1, 2-dichloroethane are mixed so as to obtain a sulfonating agent solution, reaction is carried out in ice-water bath, the grafted product is added, reaction, filtering, deionized water washing, and drying are carried out so as to obtain the sulfonic acid type aromatic block cation exchange resin. In processing of heavy metal ion containing waste liquid, the advantages are that: many adsorption sites are achieved, adsorption capacity is large, regeneration can be realized, no pollution is caused, solvent resistance is excellent, mechanical strength is high, wear resistance is high, and excellent practical using capacity is achieved.