A kind of unnamed Ir_Fe_Ni alloy was found in chromite of Luobusa ophiolite in Tibet.EPMA shows that its molecular formula is Ir0.69Fe0.28Ni0.03, and the powder X-ray diffraction data, measured by SMART APEX-CCD system, are shown as follows (inside the parentheses isI/Io): 2.188(100),1.896(90),1.347(50),1.149(80),1.096(15),0.949(5),0.874(15),0.852(15),0.773(10). According to the powder diffraction data, the crystal structure of the alloy belongs to the face-centered cubic kind of metal element. The atom coordinates are determined and the theoretical powder diffraction pattern is calculated according to the structure model. The results show that the theoretical powder diffraction pattern is basically consistent with the observable data. The crystallographic data of Ir-Fe-Ni alloy can be summed up as follows:a=3.802(4) ,space group:Fm3m,the number of molecules in unit cellZ=4,Dc =13.84 g/cm3。