In order to test the hypothesis that arbuscular mycorrhizal fungi (AM fungi) can improve growth of vegetables cultivated in protected horticulture soils which was affected by secondary salinization as a result of over-fertilization,Lactuca sativa plants growing at three soil EC levels (607,1 236 and 1 866μS cm^-1) were inoculated with Glomus intraradices (BEG141) and Glomus mosseae (BEG167).Results show that with the increase in soil EC value,the lettuce decreased in biomass,but this decrement was greater in CK than in the inoculation treatment when soil EC was low,eg.607μScm^-1.Compared with the plants in CK,the inoculated plants had a higher NO₃^- concentration at the soil EC level of 607 and 1 236μScm^-1,higher P and chlorophyll concentrations at the same soil EC level.and a higher soluble sugar concentration in the root when soil EC was 607μScm^-1,but a lower when it was increased to 1 236 and 1 866μScm^-1.The findings suggest that AM fungi can improve the growth of lettuce plants at a lower soil salt (607μScm^-1) level,but reduced the growth at a higher level (1 866μScm^-1).Its possible mechanisms are to be discussed.