Abstract: Based on the theory of coal structure chemistry, the carbon composition differences between Yongxing lignite and its demineralized sample were comparatively studied with solid state ¹³C-CP/MAS NMR analysis. The results show that the impact of mixed acid treatment demineralization on the allocation proportion of aromatic carbons and aliphatic carbons is insignificant, but its destructive effects on quaternary carbon, aliphatic carbon bonded to oxygen in cyclic hydrocarbon, aromatic bridgehead carbon and carboxyl carbon are more apparent. While aromatic bridgehead carbon is depleted, the proportion of aromatic methyl does not decrease but slightly increases simultaneously. This indicates that the double/multi-ring structures are destroyed into single-ring ones and the aromatic cluster size shrinks, which is the most critical influence of demineralization by mixed acid treatment on Yongxing lignite structure.