In a WHF-08-type reactor, three kinds of semicokes (Hongce lignite semicokes, Shenmu bituminous coal semicokes, and Jincheng anthracite semicokes) were activated with ammonia at high temperatures and high pressures. Results showed that the catalytic activity of the semicokes was significantly enhanced after activation. It was observed that the conversions of methane and carbon dioxide increased with increases in the concentration of ammonia and the activation temperature and increased and then stabilized as the activation time increased. It was also observed that the activation pressure had relatively weaker effects on the re-forming reaction and the optimal conditions were as follows: 8% ammonia, 300 degrees C, 6 MPa, and 3 h. The surface structures of semicokes before and after activation were characterized. The results showed that the content of -NO2, -NH2, -CN, and other basic groups increased while the content of acidic groups decreased after activation, and the TNB of the three kinds of semicokes improved to 0.373, 0.325, and 0.249 mmol g(1), respectively, which increased the number of active centers of semicoke and promoted the adsorption of methane and carbon dioxide on the surface of semicokes.