In recent years, tumor-infiltrating B lymphocytes (TIL-B) play a complex and important role in tumorigenesis and tumor development. TIL-B contains various subpopulations, which can be broadly classified into subpopulations of tumor-suppressing B cells, such as antigen-presenting B cells and plasma cells; and subpopulations of tumor-promoting B cells, such as regulatory B cells (Bregs). The anti-tumor mechanisms of TIL-B contain many aspects, including the secretion of specific antibodies such as IgG and IgA; activation of T cells through antigen presentation; release of cytokines that affect tumor cell growth; direct killing of target cells through the Fas/FasL and perforin pathways; and enhancement of anti-tumor immunity through interactions with T cells. The pro-tumor mechanism of TIL-B also includes many aspects, such as Bregs can inhibit anti-tumor immunity by secreting cytokines, inducing the production of regulatory T cells (Tregs), and inhibiting the interaction between T cells and antigen presenting cells (APCs). Atypical memory (AtM) B cells and leucine-tRNA-synthase-2 (LARS2) -expressing B cells (LARS B) can also promote tumor progression by secreting cytokines such as TNF-α and TGF-β. Based on the above mechanisms, a variety of tumor therapies are now available. Firstly, the anti-tumor effect of TIL-B can be enhanced. Immune checkpoint blockade therapy is a classical immunotherapy method, and TIM-1 is a key checkpoint and has achieved certain efficacy. In addition, the development of suitable novel antibodies, safe and effective TIL-B vaccines are also promising therapeutic methods. Adoptive metastatic B-cell therapy, direct activation of B-cells, chemotherapy and targeted drugs is limited because of the high technical requirements, high toxicity and uncertainty of efficacy. In the future, it is expected that further research will gradually expand the scope of its application to achieve more effective treatment for tumor patients. Selective depletion of B cells is an immunotherapy based on the inhibition of Bregs subpopulations to achieve anti-tumor effects. The next step is to develop more efficacious targeted drugs by understanding the phenotypic and functional differences of Bregs. Finally, TIL-B can be involved in the treatment and prognosis of tumors as a predictive tumor immune marker. The efficacy of treatment can be simply assessed by observing TIL-B distribution and density in tumor. Stress-responsive memory B cells and tumor-associated atypical B cells (TAAB) have clearly shown to be associated with shorter and longer survival in cancer patients, thus being used as biomarkers of immunotherapeutic response in human cancers. This paper reviews the current status of TIL-B research, summarizes its mechanism of action in tumor immunity, analyses current therapeutic strategies and prognostic assessment methods. Future focus on understanding the functional heterogeneity and molecular regulatory mechanisms of TIL-B is essential for optimising tumor immunotherapy strategies. The systematic study of TIL-B characteristics and mechanisms of action in different tumor types can help provide a theoretical basis and potential targets for the development of new tumor therapeutic strategies.