In order to reveal the relationship between plant diversity and AM fungi, the diversities of vegetation and AM fungi in three subtropical grassland ecosystems were investigated. Results indicated that there was no significant difference between AM fungi diversities of three grasslands, but significant difference was observed between plant diversities, with the Shannon-Weiner diversity indexes of 0.460, 0.614 and 1.703, respectively. The spore densities of three grasslands were 4.7, 2.1 and 5.2 g~(-1), respectively. This indicated that plant diversity was higher in the grassland with higher AM fungal spore density. The coefficient between plant diversity and spore density was 0.658(P<0.01), and that between plant species richness and spore density was 0.543(P<0.05). The present research showed that spore density is one important AM fungal factor influencing plant diversity