To investigate the effect of mesoporous carbon nanospheres （MCS） on the thermal decomposition properties of cyclotrimethylenetrinitramine（RDX）， MCS was prepared by double template method with the particle size of about 350 nm. RDX crystals were introduced into the pore and surface of MCS by host-guest chemistry technology. The morphology and structure of MCS and MCS/RDX composite were characterized by scanning electron microscopy （SEM） and X-ray powder diffraction （XRD）. The interface interaction between MCS and RDX was studied by Fourier transform infrared spectroscopy （FTIR） and differential scanning calorimetry-thermogravimetry （DSC-TG）. Compared with pure RDX， the decomposition temperature of MCS/RDX composite decreased by 13 ℃ and the heat release increased. The apparent activation energy decreased from 234.87 kJ·mol^-1 to 126.48 kJ·mol^-1. The sensitivity tests were carried out by the drop hammer impact sensitivity instrument and the electrostatic spark device. Compared with the pure RDX， the impact sensitivity and electrostatic spark sensitivity of the obtained MCS/RDX composite are apparently reduced. Therefore， the obtained MCS has good catalytic performance for the thermal decomposition of RDX and can reduce the sensitivity of RDX.