Fine roots played a significant role in exerting the plant functions,soil carbon pool and global carbon recycling.We observed biomass,production and turnover of the fine roots of alfalfa by container method and minirhizotron in the whole growing season that was ranged from June to October in 2013.The result showed that:(1)The inoculated Glomus mosseae (Gm) had the highest mean biomass (12.46 g·m^-2),the control group had the lowest mean biomass (7.31 g·m^-2).The live fine root biomass peaked in mid September,but the dead showed a tendency of increasing first and then declining,and then increasing.In the whole growing process,the dead fine root biomass of non-inoculated was higher than that with inoculated treatment,and inoculated Glomus intraradices (Gi)showed the lowest biomass of dead fine root (3.11 g·m^-2).(2)Inoculated Glomus etunicatum (Ge) had the highest fine root production (0.045 mm·cm^-2·d^-1),Gm and control group had the lowest (0.027 mm·cm^-2·d^-1).However,fine root mortality of non-inoculated treatment (0.044 mm·cm^-2·d^-1) was significantly higher than that with inoculated treatments,and Gi had the lowest fine root mortality (0.021 mm·cm^-2·d^-1).(3)Production and mortality peaks of fine roots appeared at the end of August and October,but trough came in at the end of September to mid October and the end of June to August during the growing reason.The average fine root length and annual length production of Glomus versiforme (Gv) was significantly higher than that of control and other inoculated treatments.Control treatment had the highest fine root turnover,Gv and Gm were the lowest.Inoculating with arbuscular mycorrhizal fungi could improve fine root biomass,reduce mortality and increase the lifespan of alfalfa.