Despite the evolution of aggressive surgical techniques, extensive methods of supportive care and a vast array of anti-microbial options, intra-abdominal infection (IAI) is still a challenging clinical issue. Especially, when progressed IAI with septic complications because of unbalanced immune responses, the prognosis will deteriorated significantly. Recent studies indicate that besides the natural immunological cells, including macrophages and neutrophils, local immunological characteristics of peritoneal cavity should be studied with great attention. Among them, the omentum is considered to be a visceral adipose tissue with unique immune function. The milky spots(MSs) formed by the accumulation of immune cells performs immune surveillance and has a lymph node-like immune function, which is very important for the immune defense of the abdominal cavity. B1 cells and two types of intrinsic lymphocytes(ILC2) in the peritoneal cavity, although belonging to the lymphatic lineage, may play an important role in abdominal infections, especially in the early stages of the disease, due to their rapid responsiveness and acquired immune function. Therefore, paying attention to the immunological characteristics of the peritoneal cavity, and elucidating the changes, functions and regulatory mechanisms of B1 cells and ILC2 around the MSs and their components in the process of IAI, in order to explore the immunomodulation targets of blocking the infection from local to systemic dissemination, may be the key to solving the clinical problem of severe IAI and improving prognosis.