Due to the high melting point, excellent high temperature strength and anticorrosive property, iridium is the unique material which can be used under extremely hostile environments. However, iridium exhibits an anomalous brittle fracture behavior, a mixed brittle intergranular fracture (BIF) and brittle transgranular fracture (BTF), even though it is of face-centred cubic (fcc) crystal structure. A great deal of efforts have been made to explore the embrittlement mechanisms since the anomalous fracture behavior was recognized in 1960 s, up to now, there has not been a reasonable conclusion yet. This paper emphatically reviewed the possible embrittlement mechanism of iridium, including impurity-induced brittleness, intrinsic brittleness and special defect structure induced embrittlement, discussed the research status quo about the deformation and failure mechanisms of iridium. Finally, the research direction and research method of the embrittlement mechanism of iridium were forecasted