Carbon-encapsulated Fe–Ni alloy nanoparticles were synthesized through detonation using safety composite explosive precursors doped with Fe (NO3)3? 9H2O and Ni(NO3)2?6H2O. The morphology, components, and structure of the synthesized carbon-encapsulated alloy nanoparticles were characterized through X-ray diffraction studies, Raman spectroscopy and Transmission electron microscopy attached with energy dispersive X-ray spectroscopy (EDS). Results showed that the carbon-encapsulated Fe–Ni nanoparticles with a core–shell structure. The grains exhibited sizes ranging from 40 nm to 60 nm and were uniformly distributed. The encapsulated metal core was mainly composed of different proportions of Fe and Ni. The outer shell was composed of graphite and amorphous carbon, also there were onion carbon formed by the graphitization of diamond clusters in the vicinity of the nanoparticles. The electromagnetic characteristics of Fe–Ni alloy nanoparticles composites were measured by Agilent microwave network analyzer in the band of 2～ 18 GHz. The experimental results show that, 2 mm in thickness reflection loss R(dB) of the nanoparticles which the atomic ratio of iron and nickel is 1: 4, the absorption layer has double absorption peak, peak values are -14.6dB (9.7GHz) and -7.7dB (14.3GHz), the absorption band ranges of -10dB is from 8.5 to 11.8GHz. The reflection loss R(dB)of the nanoparticles which the atomic ratio of iron and nickel is 1: 1, 2 mm in thickness reaches to 30 dB at 12.88 GHz, the absorption band of -10dB is 9.7 ~ 14.4GHz, which has wide absorption band and excellent absorbing property.