Tumor microenvironment (TME) is a highly intricate and variable system. The Warburg effect has made researchers further realize that TME is a highly hypoxic microenvironment. Currently, it is reported that lactate is not merely a metabolic waste but also serves important biological functions, which provides a large number of reaction substrates for lactylation. Post-translational modification (PTM) is crucial for signaling and physiological regulation in both normal and cancer cells. Various PTMs play pathological roles in tumor proliferation, metabolism, and the remodeling of the tumor immunosuppressive microenvironment (TIME). Lactylation, as a newly reported PTM, plays an important role in shaping TIME and aggravating tumor immunotherapy resistance. Numerous studies have demonstrated that histone lactylation can directly stimulate gene transcription within chromatin, thereby contributing to tumor promotion and diminishing the efficacy of therapeutic agents against tumors. Advancements in multi-omics technology enable researchers to investigate lactylation-related substrates more effectively. By precisely targeting these sites, it is possible to reduce histone lactylation in order to mitigate their effects on tumor immune resistance. Despite the existence of numerous studies, there remains a notable deficiency of systematic reviews in this field. Therefore, this review focuses on the novel mechanisms of lactylation that promote tumor progression and its impact on tumor immune resistance. Finally, we propose relevant therapeutic regimens for reversing lactylation to guide tumor combined therapy, thus providing benefits upon more patients with tumor immune resistance.