This study investigated the reaction behavior of oil sand bitumen from Inner Mongolia using a fluid-bed thermal reactor. The optimal temperature and reaction time were obtained. The results showed that the fluid thermal reaction was a feasible carbon rejection process that could be used to obtain high-quality liquid products from oil sand bitumen. The structures of bitumen and their liquid products derived from fluid thermal conversion were analyzed using an infrared spectrum and proton nuclear magnetic resonance techniques, and the average structural parameters were determined using the modified Brown-Ladner method. In comparison to native bitumen, the average structural parameters of liquid products were significantly changed. For different oil sand bitumen, the structural changes revealed a similar tendency for the coking formation of polycyclic aromatics and the cleavage of long paraffin side chains during fluid thermal conversion.