The influence of aeration condition on lactic acid production with distiller's grain by open fermentation was investigated. It was found that incompletely aerobic condition would do good to lactate fermentation without pre-saccharification by relative enzymes. In this study, with the previous 24 hours' air supply, the highest lactic acid concentration could reach to 15.45 g/L, whereas it was about 12.1g/L under completely anaerobic condition. However the complete aerobic will decrease the lactic acid generation as Lactobacillus casei is anaerobic. The preliminary reason for the improvement was there existed some aerobic microorganism able to decompose fibrin in the distiller's grain into reducing sugar, which could be supplied to the lactate bacterial to produce lactic acid.