Lactic acid was previously regarded as a metabolic waste product with no biological function. As lactic acid has been intensively studied, it has been found to have multiple roles. Lactation modification is a recently discovered protein post-translational modification process related to lactic acid. There are two main types of lactation modification:one is direct modification related to lactic acid and the other is indirect modification related to pyruvate. Both types of lactation modification may be regulated by various aspects such as glycolysis, lactate transport and accumulation, protein crosstalk, and the nervous system. Lactation modification can play an important role in metabolic reprogramming, proliferation, migration, and immune escape of tumor tissues by directly or indirectly modifying histones or non-histone proteins. The in-depth study of lactation modification is expected to find new pathways for tumor diagnosis and treatment. Therefore, in order to clarify the research progress of lactation modification in tumors, this paper presents a review on the molecular mechanism of protein lactation modification and the research progress of its role in tumors.