Abstract: The purpose of this study is to investigate the fluidized preheating characteristics, combustion characteristics and pollutant emission characteristics of semi-coke in preheating combustion technology based on a circulating fluidized bed (CFB). Combustion experiments of Yulin semi-coke fired at the 30kW oxy-fuel combustion experimental facility with solid-fuel preheated by CFB under different preheating oxygen concentration atmospheres including air, 21% O₂/CO₂, 23.9% O₂/CO₂, and 27.1% O₂/CO₂, are performed. The modified ratio of semi-coke under different preheating atmospheres, and its NO_x emissions regulation under the O₂/CO₂ atmosphere are analyzed. The results show that the preheating process could increase the Brunner-Emmet-Teller (BET) surface area of semi-coke to 30 times that of the original BET surface area. The BET surface area of the fuel after preheating modification in an O₂/CO₂ atmosphere at the same temperature is approximately 1.3 times that of the air atmosphere. The calorific value of preheated coal gas produced in an O₂/CO₂ atmosphere is 2.25 times that of preheated coal gas produced in an air atmosphere. The preheating process has little effect on the graphitization degree and reaction active site ratio of semi-coke. Under the high oxygen concentration in the combustion zone, the NO_x emissions increase with increasing oxygen concentration of preheating unit. Oxy-fuel preheating combustion technology is more advantageous for the gas-phase modification of ultralow volatile carbon fuels. A high preheated oxygen concentration is beneficial to semi-coke modification, but not conductive to NO_x control.