The invention discloses a preparation method and application of a polydopamine modified polystyrene-ethylene glycol dimethacrylate porous organic polymer. The preparation method comprises the steps of preparing polydopamine modified polystyrene-ethylene glycol dimethacrylate, and preparing the polydopamine modified polystyrene-ethylene glycol dimethacrylate porous organic polymer. Polydopamine modified polystyrene-ethylene glycol dimethacrylate is prepared by virtue of a reverse micelle swelling method, styrene is taken as a monomer, ethylene glycol dimethacrylate is taken as a cross-linking agent, polyvinyl alcohol is taken as a pore-foaming agent, and finally, a porous organic polymer particles is synthesized. The polydopamine modified polystyrene-ethylene glycol dimethacrylate porous organic polymer is prepared through coating and modification of polydopamine, and the hydrophilic performance, mechanical property and adsorption performance to biomacromolecules such as polypeptides, proteins and polysaccharides of the porous organic polymer are obviously improved.