The invention discloses a preparation method of PCV2 (Porcine Circovirus2)-D. The microorganism preservation number of PCV2 (Porcine Circovirus2) is CGMCC (China General Microbiological Culture Collection Center) No.7245. According to the preparation method, the preference of genetic codon of the PCV2 is modified, and the preferred codon is modified into non-preference codon, so that the expressions of the components of the virus are reduced, further, the copy rate of the virus in host cells is lowered, the virus is weakened, and the PCV2-D is obtained by genetic modification. Furthermore, the proliferation speed of the PCV2-D is compared with that of wild type strains at a cellular level. The detection of PCR (Polymerase Chain Reaction) and IFA (Indirect Immunofluorescence Assay) prove that the PCV2-D can be infected and copied in cells, and has certain infection.