The invention belongs to the technical field of cation exchange resin and discloses a crosslinked lignosulfonic acid based cation exchange resin as well as a preparation method and application thereof. The method comprises the steps: carrying out an aldol condensation reaction on sulfite, ketone, lignosulfonate and aldehyde to obtain an active polycondensate; and adding a crosslinking agent for athermal insulation curing crosslinking reaction to obtain the crosslinked lignosulfonic acid based cation exchange resin, wherein the dosages of all the components are calculated in parts by mass: 3-8parts of sulfite, 4-10 parts of ketone, 5-15 parts of lignosulfonate, 5-15 parts of aldehyde and 2-5 parts of crosslinking agent. According to the resin disclosed by the invention, not only is the ketone sulfonated to introduce a great number of sulfonic acid groups, but also lignosulfonate also contains a great number of sulfonic acid groups, and therefore, the product is high in sulfonated group content, can be used as a biomass-based strongly-acidic cation exchange resin, has the characteristics of high exchange equivalent weight and relatively low cost, can be used in the field of industrial water treatment and can be particularly applied as a strongly-acidic cation exchange resin to the removal of calcium and magnesium ions in hard water.