Abstract: The aim of this study is to isolate a nitrogen-fixing strain of producing high-yield polysaccharide from the cultivated maize soil samples around the Long-term Positioning Experiment Station of Brown Soil in Shenyang Agricultural University，and to study the strain identification，the optimization of culture conditions，and the relationship between nitrogen fixation and sugar production. The identification of the strain was carried out by morphological observation and molecular biology. The growth and culture conditions of the strain were determined by analyzing microbial biomass via enzyme mark instrument. The relationship between nitrogen fixation and sugar production was analyzed by measuring OD600 and polysaccharide yield. Results showed that the strain was Bacillus aryabhattai and named as WN-F. WN-F strain reached its highest growth at 37℃ and 180 r/min for 12 h. The medium was optimized as the formula（L-1）：sucrose 20 g，beef extract 2 g，KH2PO4 0.4 g，MgSO4 · 7H2O 0.4 g，NaCl 0.4 g，CaSO4 · 2H2O 0.4 g and CaCO3 2 g. The polysaccharide yield of strain WN-F showed a parabolic relationship with the increase of initial nitrogen concentration，and the proper carbon nitrogen ratio promoted the synthesis of extracellular polysaccharide. B. aryabhattai WN-F is a dominant strain in maize soil for long-term positioning experiment. High-yield extracellular polysaccharide has a nitrogen fixation effect，thus，it is a candidate strain for applying combined nitrogen fixation of maize and reducing fertilizer application.

Key words: Bacillus aryabhattai, nitrogen fixing, extracellular polysaccharide, optimization of culture condition