Coking of three model compounds of hydrocarbon fuel-n-heptane, cyclohexane, and tricyclo[5.2.1.0(2.6)]decane (JP-10)-during their thermal cracking processes under supercritical condition (873.15 K, 4.1 MPa) has been investigated. The product distributions of the thermal cracking are analyzed by gas chromatography-mass spectrometry (GC-MS). The morphology and microstructures of the cokes are characterized by the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The results show that chemical structures play important roles in the thermal stability and coking property of the fuels. The thermal cracking conversion of n-heptane is highest, and the coke yield of JP-10 is highest under the same conditions. It is interestingly observed that the morphologies of the cokes produced from the thermal cracking of three fuels are quite different, which from n-heptane, cyclohexane, and JP-10 are in the forms of carbon nanofilaments, carbon nanotubes, and irregular carbon particles, respectively.