Oil shale semicoke produced from the oil shale retorting process causes great hazards to the environment due to its high phenol and polycyclic aromatic hydrocarbons content. A good solution of the current of semicoke is to burn it as feedstock. In the present work, the extremely low calorific oil shale semicoke of 2384 kJ/kg was adopted, and a series of experimental investigations and computational analyses were carried out in bench-scale and pilot-scale bubbling fluidized bed combustors, to understand its combustion characteristics. Results indicated that by adopting effective technique means, the extremely low calorific oil shale semicoke could be directly burnt in the fluidized bed combustor, and the combustion was completely relying on its heat release. The main influence factors of combustion stability were combustion temperature, fluidization air temperature, and burnout rate. However, within the scope of test parameters, its combustion characteristics were mainly affected by dense-bed temperature, fluidization air velocity, and grain size, and less affected by static bed height. Furthermore, its comprehensive utilization system was put forward, and the general configuration and technical data of 35 t/h medium pressure fluidized bed boiler adopting the mixture of fine oil shale and extremely low calorific oil shale semicoke whose calorific value is 2876.2 kJ/kg were also given at the end of this article.