Group 3 innate lymphoid cells (ILC3) are an ILC subset that is characterized by the expression of retinoic acid-related orphan nuclear receptor γt (RORγt) and interleukin 22 (IL-22). This review summarizes the role of ILC3 in coordinating innate immunity and adaptive immunity based on current research and elaborate the significance of ILC3 from the perspective of immune system evolution. In addition, based on immune-related functions, we propose a possible time when ILC3 appears in the evolution of the immune system. And then, the research limitations and prospects are discussed.