Abstract: Breeding of nitrogen-fixing bacteria is the basis for nitrogen-fixing microbial fertilization. A high efficiency nitrogen-fixing bacteria Sphingomonas GD542 was isolated from maize rhizosphere — a short rod of 0.4 mm×1.0~1.5 mm, G-, with 5.046 nmol (C₂H₄)·h^-1·mg^-1(protein) nitrogenase activity, that can grow from 4 ℃ to 37 ℃ and resistant to 10% NaCl. Phylogeny based on 16 S rDNA sequence shows that GD542 shares 96% DNA homology with S. azotifigens. Based on the analysis results of morphology, physiology, chemical property, and 16 S rDNA sequencing, strain GD542 is identified as Sphingomonas sp. Green house test shows a statistically significant increase in dry weight and nitrogen content in pakchoi inoculated with GD542 strain, indicating high nitrogen fixing ability of GD542 strain. There is 206% increase in dry weight and 230% increase in plant nitrogen content of pakochoi compared with the control. Hence GD542 strain holds a good prospect for future applications.