[Background] Robinia pseudoacacia ‘Hongsen’ is a fast-growing deciduous tree of Robinia in Leguminosae. Endophytic diazotrophic bacteria of Robinia pseudoacacia ‘Hongsen’ is being researched little nowadays. [Objective] We studied the diversity and growth promoting characteristics of the culturable endophytic diazotrophic bacteria isolated from Robinia pseudoacacia ‘Hongsen’. [Methods] Strains were isolated and purified from surface sterilized roots, stems, leaves and root nodules of Robinia pseudoacacia ‘Hongsen’, the isolates were clustered by using IS-PCR finger-printing, nitrogenase activity of the representative strain of each group was measured, we also conducted phylogenetic analysis of 16S rRNA gene, physiological and biochemical tests and growth promoting experiments of the representative strains. [Results] A total of 56 strains were isolated from Robinia pseudoacacia ‘Hongsen’, belonging to ten groups: Paenibacillus sabinae, Klebsiella michiganens, Kosakonia radicincitans, Kosakonia pseudosacchari, Mesorhizobium erdmanii, Mesorhizobium huakuii, Mesorhizobium silamurunense, Pseudomonas geniculate, Burkholderia territorii and Devosia riboflavina, in which 5 groups were associative nitrogen-fixing bacteria, 3 groups were symbiotic nitrogen-fixing bacteria, 2 groups had not the nitrogen-fixing ability, which showed the rich diversity of endophytic diazotrophic bacteria of Robinia pseudoacacia ‘Hongsen’. Growth promoting experiments showed that 7 groups had the function of phosphorus solubility, 6 potassium solubility, 6 auxin secretion, 6 siderophore production, and 2 proteases production. [Conclusion] Endophytic diazotrophic bacteria isolated from Robinia pseudoacacia ‘Hongsen’ have abundant genetic diversity and growth promoting characteristics, which have potential value in exploitation and utilization of agricultural microbial fertilizer.