The modification of noncaking lignite to coking coal was carried out using a CO-subcritical water reaction system, and the surface structure of the modified coal was characterized by X-ray photoelectron spectroscopy. The results show that the caking index (G) of the modified coals increases from 24 to 92 during the progress of catalytic hydromodification. Some oxygen-containing functional groups were removed, decreasing the concentration of C-O, C=O, and COO-.