The co-gasification characteristics of petroleum coke (PC), hydrochar (PS), and their blends with different ratios were studied by using thermogravimetric analysis. The Coats–Redfern model was employed to calculate the gasification activation energies of different samples. The results manifested that the gasification process of PS and blends could be classified into two stages: pyrolysis and char gasification, but for PC, there was only one primary char gasification stage. The activation energy of the pyrolysis stage was significantly smaller than the char gasification stage. In the latter stage, with the increase in the ratio of PS from 20% to 80%, the activation energy was reduced from 114.1 kJ/mol to 82.8 kJ/mol, which indicated that the PS had a significant promoting influence on the PC gasification. The research results can provide a theoretical guiding significance for the efficient use of PS and PC.