Hydrogasification of Inner Mongolian lignite semicoke was investigated at varying operational conditions: grain size of 0.15-0.7 mm, hydrogen flow rate of 300-1500 mL/min, temperature of 700-900 degrees C, pressure of 0.1-5.0 MPa, and heating rate of 10-30 degrees C/min, using a self-developed high-temperature and high-pressure fixed-bed reactor with a design parameter of 1000 degrees C and 12 MPa. The reaction characteristics and mechanism of semicoke hydrogasification were discussed. The results showed that, at a grain size of semicoke of <0.25 mm and a hydrogen flow rate of >1200 mL/min, the effects of internal and external diffusion resistances were basically eliminated; the increase of the pressure or heating rate exerted a positive influence on the hydrogasification of semicoke. The optimum reaction conditions were as follows: grain size of 0.25-0.35 mm, hydrogen flow rate of 1200 mL/min, temperature of 800 degrees C, and pressure of 3.0-4.0 MPa. During hydrogasification, the fracture of alkyl side chains, hydrogenation/methanation of carbon (e.g., C + 2H(2) = CH4), and hydrogenation of oxygen-containing structures were accelerated. Three stages occurred during hydrogasification of Inner Mongolian lignite semicoke: hydropyrolysis stage, rapid hydrogasification stage, and slow hydrogasification stage. Moreover, the reaction characteristics of each stage were quite different because of distinct carbon structures.