Cancer is a serious threat to human health and is the most interesting research field at present. Compared to conventional treatments, tumor immunotherapy has a unique advantage in cancer treatment, favored by more and more outcomes from research or clinical trials of institutions and pharmaceutical companies, which is showing a booming trend recently. Due to the complexity of the immune system, tumor immunotherapy covers a variety of mechanisms and approaches, including immune checkpoint inhibition, vaccine-based therapies, adoptive T cell transfer, and therapeutic antibodies. Through the investigation of a large number of literature and database information, this paper focuses on the mechanisms and applications of current immunotherapies, aiming to explain the general trend and direction of tumor immunotherapy development.