The effects of elevated CO_２ on the species diversity of arbuscular mycorrhizal fungi （AMF）in roots of various species of host plant were studied under pot culture condition in greenhouse. Twelve common cover plants in subtropical orchards were selected as host plants of AMF colonization in this research. These twelve host species were grown at ambient (350μmol mol^－１) and elevated CO_２ (ambient + 350μmol mol－１) concentrations in growth chamber, respectively. The plants were sampled at 180th day after seedling and DNA of AMF in plant roots was extracted by CTAB method. The partial rDNA sequence encoding ribosomal 28S big unit was amplified with special primers U1/U2 for fungi, and PCR products were analyzed with denaturing gradient gel electrophoresis （DGGE）. Species diversity was presented by using Shanno-Weiner diversity index. AMF colonized in roots of 12 host plant species were divided into two different groups, unique species (US) group and common species (CS) group. Results showed elevated CO_２ could enhance species numbers of AMF in US group but reduced that in CS group.Under elevated CO_２ condition species diversity of AMF community colonized in Zea mays, Amarathus spinosus, Glycine max, Oryza sativa, Echinochloa crusgalli var mitis and Lolium perenne decreased by the corresponding percentage of 27.12%, 16.84%, 10.12%, 8.62%, 8.58% and 2.67%, while that in Trifolium repens, Eleusine indica, Poa annua, Gnaphalium affine, Avena fatua and Plantago virginica tended to increase by 76.26%, 28.50%, 17.60%, 15.08%, 1.46% and 0.96%, respectively. The average biodiversity index of AMF colonized in the roots of all 12 plants tended to increase when CO_２ concentration increased from 350μmol mol^－１ to 700μmol mol^－１. These results also indicated that the response of species diversity of AMF community to atmospheric CO_２ enrichment largely depended on characteristics of host plant. Biennial plants, including Avena fatua, Plantago virginica, Poa annua, Trifolium repens and Gnaphalium affine increased AMF diversity (with the exception of Lolium perenne), while annual plants Zea mays, Amarathus spinosus, Oryza sativa, Glycine max and Echinochloa crusgalli var.mitis decreased it. (except Eleusine indica).