In the paper, the condition of steady gaseous detonation and detonation product composition were analyzed theoretically. Nano carbon material and carbon coated iron nano particles were prepared by gaseous detonation method with oxygen and benzene, oxygen and benzene dissolved ferrocene, respectively. Characterized by X-ray diffraction and transmission electron microscope, it can be found that carbon nano materials are spherical or quasi-spherical, particle size ranges in 10~30nm, and dispersity is poor. The cluster area is mainly amorphous carbon, while a few of onion-like fullerenes in dispersing region. The molar ratio of free carbon and iron has an influence on morphology and structure of carbon coated iron nanoparticles. When the molar ratio value ranges in 10~28, carbon coated iron nanoparticles can be prepared, which are spherical, with a clear core-shell structure and good dispersion; when the value greater than 50, carbon coated iron morphology is changed and part of carbon with a sheet structure.