The bromodomain and extra-terminal (BET) proteins act as "readers" for lysine acetylation and facilitate the recruitment of transcriptional elongation complexes. BET protein is associated with transcriptional elongation of genes such as c-MYC and BCL-2, and is involved in the regulation of cell cycle and apoptosis. Meanwhile, BET inhibitors (BETi) have regulatory effects on immune checkpoints, immune cells, and cytokine expression. The role of BET proteins and BETi in a variety of tumors has been studied. This paper reviews the recent research progress of BET and BETi in hematologic tumors (mainly leukemia, lymphoma and multiple myeloma) from cellular level studies, animal studies, clinical trials, drug combination, etc. BETi has a promising future in hematologic tumors, and future research directions may focus on the combination with other drugs to improve the efficacy.