The effects of four culture substrates (vermiculite,vermiculite-soil，sand- vermiculite,sand-soil) on the symbiosis of different varieties of soybean and AM fungi (Rhizophagus irregularis) were studied with pot culture. The dyeing effects of parker pure black ink and trypan blue on soybean mycorrhiza were compared. The application of magnified grid intersection method and Trouvelot fiveclass classification method for detecting largescale mycorrhizal symbiosis structures were explored as well. The results showed that vermiculite and soil (V∶V=4∶1) was more conducive to the infection of AM fungi with soybean. The arbuscular abundance,hypha density and vesicle abundance in this culture substrate are significantly higher than those in other substrates,indicating that it can be used as the best culture substrates for soybean and AM fungi symbiosis. Currently,the ink staining and the magnified grid intersection method are the best methods for detecting large-scale mycorrhizal symbiosis structures.