The invention provides a detection method of lactic acid in baijiu base liquor. The detection method comprises following steps: low temperature reduced pressure distillation is adopted for complete evaporation of a baijiu base liquor sample; a low concentration ethanol aqueous solution is added for redissolving of the evaporated sample; and then high performance liquid chromatography detection is carried out. According to the detection method, a simple pretreatment method is adopted; a high performance liquid chromatograph is used for direct sample injection; the content of lactic acid in baijiu base liquor can be obtained accurately; the detection method is rapid, is high in accuracy, and wide in detection concentration range; influences of compounds such as esters, other organic acids, and higher alcohols in baijiu base liquor can be eliminated; and the detection method is of important significance in scientific guidance on baijiu base liquor production.