In present study ， the high-yielding fermentation medium for strain K 2 (Clostridium celerecrescens) producing caproic acid (CA) was screened , and the saccharide s , nitrogen source, the growth curve, CA-producing curve , single-factor tests, orthognal tests and verificati ing test for optimizating conditions were carried o ut. The results demonstrated that sodium acetate cultur medium was the best one among the four candidate medium tested , and the saccharides and nitrogrn source for the fermentatio n medium were glucose and yeast extracts respective ly, the relatively important factors for CA-producing ,whic h judged from the results of single-factor test wer e glucose ， ethanol ， KCl, sodium acetate ， temperature and PH value , and the further L18 (3 6 ) orthogonal experiment indicated that the high-yielding CA fermentation conditions were: temperature 34 °C , PH 9, 0.25g / L glucose, 10mL / L ethanol , 20g /L of sodium acetate, 2g /L KCl, the optimized caproic acid-yielding was10.23±0.74(g / L ) ， which was more than the output of before optimization 7.30 ± 0.359 (g / L) 40.1%.