The effects of several factors, including fuel mixing ratio fed into boiler, bed temperature, primary air ratio, on burnout characteristics of mixed fuel of petroleum coke and oil shale were investigated at a 1 MW circulating fluidized bed (CFB) test apparatus at Xi’an Thermal Engineering Research Institute. Meantime, the effect of the fuel mixing ratio and Ca/S molar ratio on SO2 emission during co-combustion of petroleum coke and oil shale were studied. The results show that preferred mixing ratio of petroleum coke over oil shale is between 4:6 and 5:5, and primary air ratio is about 55% to accomplish favorable burnout of the mixed fuel. The combustion efficiency is higher than 97%. The increase in oil shale share in the mixture helps to improve the desulfurization efficiency during co-combustion. There is an optimum Ca/S molar ratio to achieve the highest desulfurization efficiency for co-firing the petroleum coke and oil shale. SO2 emission during co-combustion of petroleum coke and oil shale can meet the environmental requirement.