The reaction evolution process of shelled explosive charge structures under non-impact ignition conditions is highly complex， influenced by the coupling of multiple physical mechanisms such as crack propagation， gas-phase flow， and reaction propagation. To deeply reveal the laws of this reaction evolution， a calculation method for crack network expansion based on reaction pressure and the fracture toughness of the explosive matrix is proposed， targeting the coupled mechanism of crack propagation-gas-phase flow-reaction propagation. On this basis， combined with the energy conservation relationship during the reaction evolution process， a combustion crack network model for shelled explosive charges considering the physical mechanism of crack network formation is established. The accuracy of the model is verified by comparing and analyzing experimental results from existing studies. The model is used to investigate the formation of combustion crack networks， the dynamic expansion process， and the reaction-induced pressure rise behavior of the explosive charge during reaction evolution. It quantitatively reveals the coupling relationship between reaction pressure， combustion crack network area， and the average fragmentation size of the explosive matrix. Under typical working conditions of spherical charges with strong confinement， when the reaction pressure exceeds 1000 MPa， the degree of explosive fragmentation changes minimally with further increases in reaction pressure. The results show that confinement strength is a key factor determining crack propagation and pressure evolution during ignition reactions. Changing the charge size mainly affects the crack network area， while the initial ignition pressure has little impact on the final reaction outcome. In experiments with charges equipped with pressure relief holes， a phenomenon may occur where the competition between combustion-induced pressure buildup and pressure relief-induced depressurization reaches a stalemate.