Biomass pretreatment is a promising technology for reducing pollutants emitted by coal power plants and reducing coal usage. Pretreatment technologies (e.g., torrefaction, ashless and multi-pretreatment, which greatly improves less technology) alter the physicochemical properties of raw biomass, such as empty fruit bunch (EFB), and affect its combustion characteristics. In this study, the combustion and emission characteristics of two pretreated biomass fuels mixed with coal in a 500 MW tangentially fired boiler are evaluated by simulation. The results show that the pretreated fuel maintains stable combustion in the boiler under different cofiring ratios. The fuel property of the pretreated biomass fuels were changed. After torrefaction technology, Torrefied-EFB (T-EFB) had similar characteristics to sub-bituminous coal, low moisture, high volatile and faster reaction activation. Ashless-EFB (A-EFB), created after ashless pretreatment of Raw-EFB (R-EFB) with inorganic chemical deashing, maintains the essential fuel characteristics of biomass. But N, S element ash content is significantly reduced. Ashless torrefied-EFB (AT-EFB) through the ashless + torrefaction technology had similar fuel characteristics to lignite, fuel property and reaction activation was improvement. All types of pretreated biomasses with coal cofiring can significantly reduce NOX and SOX production. Compared to pure coal, NOX and SO2 emissions were significantly reduced with increasing T-EFB, A-EFB and AT-EFB substitution. The cofiring results of the three type pretreated biomasses and pulverized coal showed that, due to the high temperature of A-EFB, more thermal NO is generated, and the total NOX emission was slightly higher than that of cofired T-EFB and AT-EFB. Through the ashless pretreatment, A-EFB and AT-EFB form the SO2 emission lower than T-EFB biomass. Reason is ashless pretreatment technology can be significantly reduced biomass property S element. The pretreated biomasses can promote the ignition of pulverized coal fuel. Since A-EFB has a higher volatile content than that of T-EFB and AT-EFB, it shows a higher impact of cofiring. Simultaneously, the char burnout rate will gradually increase with the increase of cofiring ratio because the pretreated biomass generates high local temperatures, and this effect is more prominent in A-EFB. The combustion characteristics of boilers under different blending ratio conditions were analyzed by simulation, and it was found that due to the rapid combustion of T-EFB high volatile matter to generate heat, the high temperature zone inside the boiler diffused towards the burner near, but the furnace peak temperature decreased slightly. Three pretreated biomasses can promote the ignition of pulverized coal fuel. Since A-EFB has a higher volatile content than that of T-EFB and AT-EFB, it shows a higher impact of cofiring. Simultaneously, the char burnout rate will gradually increase with the increase of cofiring ratio because the pretreated biomass generates high local temperatures, and this effect is more prominent in A-EFB. The Pretreated biomass (T-EFB, A-EFB and AT-EFB) with coal cofiring could affect the heat transfer distribution in the boiler. As the temperature of the OFA burnout area decreased, the heat absorption of the water wall decreased, the FEGT increased, and the heat absorption of the heat exchange tubes increased. But the pretreated biomass cofiring conditions reduce the boiler load by no more than 6% compared with the pure coal case. To balance safe boiler operation and reduced pollutant emissions, the optimal ratio of cofiring T-EFB, A-EFB and AT-EFB with bituminous coal is 30%, 10% and 50%, respectively.