Metabolic reprogramming is a major hallmark of tumor cells. It is vital for tumor tumorigenesis growth metastasis and survival in adverse condition. Tumor cells abundantly produce lactic acid via 􀆵 aerobic glycolysis and released to extracellular microenvironment. This causes lactic acid to accumulate in the tumor microenvironment and makes it in low pH value. Recent studies revealed that lactic acid can not only be utilized as energy resources by tumor cells but also play regulated roles in tumor cells immune cells and stroma cells. In general lactic acid plays different roles in different components of tumor microenvironment. On the one hand lactic acid directly enhances the survival proliferation or migration of tumor cells by mediating metabolic reprogramming signal transduction or epigenetic modification. On the other hand lactic acid promotes tumor formation growth or metastasis indirectly by mediating angiogenesis or immune escape. In addition lactic acid - related metabolic enzymes transporters and its downstream targets significantly correlates with tumor progression which have the potential to be targeted drugs in cancer therapy. This review summarizes the recent advances in the function and mechanism of lactic acid in tumor microenvironment and discusses the future research orientation and its prospect as tumour therapeutic targets.