Drosophila melanogaster is an important model organism for understanding basic biological and human disease mechanisms. Drosophila, lacking an adaptive immune system found in mammals, can resist rapidly and effectively to infection of various microorganisms through multifaceted innate immune response involving humoral immunity, cellular immunity and melanization. The latest achievement of Drosophila immunity was reviewed in this paper, including the proteins and their interaction related to Toll and immune deficiency (Imd) signal pathway through which Drosophila produces antimicrobial peptides, and phagocytosis and encapsulation in cellular immunity and melanisation. It was showed that Toll and Imd signal pathway in Drosophila is similar to TLR4 and TNRF-1 signal pathway in human innate immune systems, respectively, which implied that the immune signal pathway of Drosophila and human may have common origins.