The effects of arbuscular mycorrhizal fungus (Glomus mosseae and G.versiforme) on the dry weight and absorbing phosphorus of Poncirus trifoliata seedlings and its root excreting organic acids under low-phosphorus stress with the Al-P as phosphorus source and poncirus trifoliata seedlings as experimental material were studied in sand culture and sterilization greenhouse.The results showed that the inoculation of AM not only markedly increased the dry weight of overground part and underground part of Poncirus trifoliata,which raised by 16.79%~135.25%,but also remarkably increased phosphorus uptake with the contribution rate up to 17.04%~71.95% (G.m>G.v).Fertilizing Al-p could observably raise the contribution rate.The kinds of organic acid which were secreted by the root systems of AM fungi inoculation were different from the control.We only detected six acids (oxalic acid,malic acid,lactic acid,acetic acid,maleic acid and citric acid) in non-inoculated treatment materials,while 7 acids (oxalic acid,tartaric acid,malic acid,lactic acid,acetic acid,citric acid,succinic acid) in G.m treatment materials,and also tartaric acid and no maleic acid detected in G.v treatment materials.Inoculation also increased the content of organic acid secretion (increased by 19.80~56.87 mg/kg) of trifoliate root,and the application of AlPO₄ greatly increased organic acid content (increased by 20.06~21.84 mg/kg);uninoculated plant root secreted a bit of organic acid;Mycorrhizal poncirus trifoliata seedlings excreted malic acid (42.87%),citric acid (39.22%) and oxalic acid (12.06%).