The invention discloses a non-food carbon source for fermentation production of lactic acid or citric acid, which is characterized in that: the non-food carbon source is used as dextrin of acorns or Chinese chestnuts of a citric acid fermentation carbon source, or used as a reducing sugar of the acorns or Chinese chestnuts of a lactic acid or citric acid fermentation carbon source, or used as the reducing sugar of gingers of a lactic acid fermentation carbon source. The preparation method comprises the following steps of: smashing the acorns, the Chinese chestnuts or the ginger roots into powder or grinding the materials to obtain pulp; adding water into the pulp to obtain pulp liquid; and liquefying by alpha-amylase to obtain the dextrin first, or further saccharifying the dextrin by using glucoamylase to obtain the reducing sugar. The raw materials for preparing the non-food carbon source are wide in source and low in cost; the preparation method is simple and convenient; equipment used is common; and when used for lactic acid or citric acid fermentation, the non-food carbon source can achieve almost the same or better effects in comparison with the food carbon sources such as corn, rice and wheat which are usually used currently, is an excellent substitute carbon source of the food carbon sources and has a high application value in industrial production.