Nucleocapsid protein(N) of avian coronavirus infectious bronchitis virus(IBV) plays an important role in maintaining viral structure and replication. The N protein produced in vitro can be applied in the fields of diagnosis, vaccination and scientific research. Expression of IBV N protein in a prokaryotic expression system has been established before, but the medium used is complex and expensive. To optimize the fermentation conditions with simpler medium, the Plackett-Burman experiment was designed for factor screening, and then response surface methodology was applied to optimize the fermentation conditions. The medium was optimized as 0.86 % polypeptone, 1.14 % yeast extract, 1.63 % NaCl, 0.02 % L-arabinose and pH 7.0. Five batches of fermentation according to the above conditions resulted in a mean value of 44.25% for the relative N protein quantity, with a 0.14 % deviation from theoretically deduced value. The fermentation conditions optimized in this study is appropriate for N protein production, which stablely expresses IBV N protein and gives a high yield.