In this study, a novel suspended ceramsite was prepared, which has high strength, optimum density (close to water), and high porosity. The ceramsite was used to feed a moving-bed biofilm reactor (MBBR) system with an anaerobic–aerobic (A/O) arrangement to treat petroleum refinery wastewater for simultaneous removal of chemical oxygen demand (COD) and ammonium. The hydraulic retention time (HRT) of the anaerobic–aerobic MBBR system was varied from 72 to 18 h. The anaerobic–aerobic system had a strong tolerance to shock loading. Compared with the professional emission standard of China, the effluent concentrations of COD and NH3-N in the system could satisfy grade I at HRTs of 72 and 36 h, and grade II at HRT of 18 h. The average sludge yield of the anaerobic reactor was estimated to be 0.0575 g suspended solid/g CODremoved. This work demonstrated that the anaerobic–aerobic MBBR system using the suspended ceramsite as bio-carrier could be applied to achieving high wastewater treatment efficiency.