The vaccine against porcine circovirus type II (PCV2) is mainly composed of virus capsid proteins. An efficient separation method of PCV2 Cap protein has not been developed. Affinity precipitation methods with high selectivity and recoverability based on the thermo-responsive affinity polymer (P-NDBN-Ni) were introduced to separate the PCV2 Cap protein. When the temperature was above the polymer LCST (36.1 degrees C), P-NDBN-Ni could be precipitated with a recovery of above 95.00%. The affinity ligand immobilized on the polymer could specifically bind the proteins. The optimal conditions for affinity precipitation were a pH of 6.0 with a ligand density of 56.22 mu mol/g polymer at 25.0 degrees C. The final results were detected by electrophoresis. The interactions between proteins and ligands were determined by the change in ligand state as seen using X-ray photoelectron spectra (XPS).