Abstract: Against the backdrop of deep peak shaving and low-load operation, the issues of stable combustion and co-combustion adaptability of low-reactivity fuels have become increasingly prominent. thermogravimetry–derivative thermogravimetry–differential scanning calorimetry (TG–DTG–DSC) was employed to investigate the combustion characteristics of anthracite (WY), coal gangue (GS), and their blends with as-fired coal (Z), bituminous coal (Y), and low-rank raw coal (H) under an air atmosphere at a heating rate of 5 °C/min. The apparent ignition temperature, T_i, was determined using the TG–DTG tangent method, and a comprehensive combustion index, S was introduced. Based on linear additivity, the theoretical ignition temperature, T_i,theo and the theoretical comprehensive combustion index, S_theo were established. The combustion behaviors represented by different indicators during co-combustion were then analyzed by considering ΔT_i, ΔS, R_S, and the evolution of DSC exothermic peak profiles.The results show that T_i mainly reflects the ignition threshold associated with the transition of blended fuels from slow oxidation to accelerated mass loss, whereas S, R_S, and DSC peak morphology more effectively characterize the reaction intensity and heat-release concentration during the main combustion stage after ignition. In the anthracite-blending system, all nine samples exhibited negative ΔT_i values, ranging from −8 to −41 °C, indicating that Z, Y, and H can all reduce the apparent ignition temperature of the WY system. However, when the WY proportion was relatively high, some samples showed a pronounced advance in T_i while still having R_S<1, suggesting a combustion behavior characterized by “marked ignition advancement but insufficient enhancement of the main combustion stage.”In the coal-gangue-blending system, T_i was mainly concentrated within 380–403 °C, and ΔT_i changed only slightly, indicating that the high-ash inert framework exerts a controlling influence on the apparent ignition onset. Nevertheless, as the blending proportion of Z, Y, or H increased, the DTG peak intensity, S, and the intensity of the first DSC exothermic peak in the 350–450 °C range increased markedly. This suggests that the improvement in co-combustion performance of the coal gangue system is primarily manifested as post-ignition combustion enhancement, rather than a substantial decrease in the apparent ignition temperature.It is indicated that, for low-volatile fuels such as anthracite, ΔT_i can serve as a sensitive indicator for evaluating ignition-promoting effects. For high-ash carbonaceous fuels such as coal gangue, however, evaluating blending performance solely based on T_i may underestimate the improvement in combustion performance. A comprehensive assessment incorporating S, R_S, and DSC peak-shape evolution is therefore recommended. These results provide a thermalanalytical basis for preliminary coal-blending screening of low-reactivity and high-ash carbonaceous fuels, as well as for evaluating their stable-combustion adaptability under low-load operation.