Graphene based materials with excellent physical properties have attracted much attention in the field of energetic materials. Notably, heteroatom doping could modify the property of graphene. Herein, nitrogen-doped graphene (NGO) with a tunable hierarchical morphology and high surface areas was prepared by a hydrothermal method. NGO composites with 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) were obtained by recrystallization in ethyl acetate. Subsequently, the catalytic activities of NGO and undoped reduced graphene oxide (rGO) on the thermal decomposition of CL-20 were investigated using differential scanning calorimetry (DSC). The decomposition temperature, self-accelerating decomposition temperature, and thermal ignition temperature of CL-20 all decrease under the influence of NGO. This is attributed to change in charge distribution of carbon atoms influenced by nitrogen dopants and more active sites induced on graphene surface. As a result, NGO exhibits enhanced catalytic effect on the thermal decomposition of CL-20.