Abstract: At present gas chromatography is considered as one of the most reliable methods in measuring lactic acid and volatile fatty acid domestically and abroad. Lactic acid and volatile fatty acid were determined respectively in general method. Lactic acid and volatile fatty acid were determined simultaneously in corn ensilage have not been reported. Using a simple and convenient method for derivative process of Methyl in this paper, a packed column was used in gas chromatography, exploring a new way of a rapid method for simultaneous determination of lactic acid and volatile fatty acid in corn ensilage to provide a reliable analysis technology for the research on corn ensilage.