Abstract: Under greenhouse conditions,the influences of eight nutrient solutions with different ratio of N to P on the growth of arbuscular mycorrhizalfungus Glomus mosseae were studied.The results showed that increasing N could improve the growth of AM fungi under certain phosphorus supplying level,but excessive N inhabited its growth.It suggests that the development of mycorrhizal fungi are influenced by N and the ratio of N to P.By comprehensive comparison of total length of external hyphae,colonized root length and spore numbers,the optimum N∶P ratio in 20% Hoagland solution for fungi growth was 4∶2.Therefore,rational regulating the N∶P ratio in nutrient solution could enhance the development of AM fungi to obtain more colonized roots,external hyphae and spores when AM fungal inoculum was produced under greenhouse conditions.