Replacing traditional solid propellants with high-energy explosives (such as hexanitrohexaazaisowurtzitane (CL-20)) is an important way to achieve microthrusters with small size and large specific impulse. In order to realize the self-sustaining combustion of CL-20, a composite propellant system with CL-20 nano-microparticles hosted in the rGO three-dimensional network is designed. Ultrafine CL-20 spherical particles (diameter 300 nm-2 μm) have been prepared by a solvent-nonsolvent method firstly, then self-supporting rGO/CL-20 fiber propellant was prepared by a dimensionally confined hydrothermal strategy. Based on the analysis of thermal analysis kinetics and combustion characteristics, it is concluded that the positive feedback mechanism of the combustion heat release of rGO/CL-20 fiber propellant plays a key role in its combustion propagation. Due to the construction of rGO three-dimensional network, the thermal conductivity of the fiber propellant is improved, and the exothermic effect of rGO/KOH can serve as the initial ignition energy for rGO itself and CL-20 microparticles. Once ignited, the combustion of high-energy CL-20 releases more heat energy than rGO, thereby forming the positive feedback mechanism. The combustion propagation speed of the prepared self-supporting rGO/CL-20 fiber propellant is 20.66 mm·s^-1, moreover, the fibrous structure facilitates the rapid modular charge of the microthrusters.