Abstract: Ammopiptanthus mongolicus (Maxim.) Cheng f. is an endangered evergreen broadleaved plant in the northwest desert zone of China. Given soil, water and other ecological factors, the authors selected Shapotou area of Zhongwei County in Ningxia Hui Autonomous Region, Alxa Zuogi, Dengkou and Wulate houqi Counties of Inner Mongolia as our research regions, where we studied the characteristics of plant communities and nodules of A. mongolicus. The plant community was rich and the components and structures were varied in different research regions because of the diversity of ecological factors. Water was the decisive ecological factor influencing the components and structures of A. mongolicus plant communities. Nodules morphology of A. mongolicus was varied. The best time to collect nodules should be earlier than the fruiting stage of its host. Nodules were in different root parts at various research regions. Water was the primary ecological factor influencing the infection of rhizobia and the generation of nodules. Nodules isolated from other legumes had similar morphology with those of A. mongolicus.