The present invention is directed to a recombinant fusion antigen gene, a recombinant fusion antigen protein and a subunit vaccine composition having the same against infection of porcine reproductive and respiratory syndrome virus (PRRSV). A recombinant fusion antigen gene, which encodes glycoprotein GP5 with truncated N′-terminal decoy epitope, a linker sequence and membrane protein M, followed by codon optimization, is expressed by a baculovirus expression system in vitro, thereby enhancing a yield of the recombinant fusion antigen protein. The recombinant fusion antigen protein can be applied in a subunit vaccine composition, for providing vaccinated animals with better protection ability without the risks of virulent spread and virulent recovery.