The invention provides a method for producing lactic acid through fermentation of acorn reducing sugar as a non-grain carbon source, comprising the following steps: preparation of the acorn reducing sugar, the selection of the strain for the dermentation production, the preparation of fermentation medium, the sterilization of the fermentation medium and the establishment of the culture conditions. The acorn reducing sugar is used as the non-grain carbon source to produce the lactic acid through fermentation, which can reach the similar even better effect as the lactic acid production through fermentation of the grain carbon source such as the common used corn, rice and wheat and the like, and have good application value for industrial production.