Generally, coal-fired incinerators are characterized by a high combustion temperature and a well-equipped flue gas cleaning system. Co-combusting municipal solid waste (MSW) in coal-fired incinerators can reduce the emission of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and help to enhance the treatment capacity of the MSW; more importantly, this approach provides a new orientation for upgrading and transitioning old coal-fired power plants. In this study, simulated municipal solid waste (SMSW) is mixed with coal in proportions of 0 (without addition), 7.5, 15, 20, and 25 wt % and then co-combusted in a drop-tube furnace. The PCDD/Fs emitted in both the flue gases and fly ashes from the combustion tests are well-investigated. In the present study, the international toxic equivalent quantity (I-TEQ) concentration of the PCDD/Fs in the flue gas can meet the emission limit (0.1 ng of I-TEQ/Nm(3)) when MSW is co-combusted at less than 20 wt %. The concentration of the PCDD/Fs in the fly ash is much lower than the permitting standard for disposal in sanitary landfill sites (3.0 ng of I-TEQ/g), and even the percentage of SMSW increases to 25 wt %. Particularly, a proper ratio of SMSW in a coal (7.5 or 15 wt %) can increase the burnout efficiency of organic carbon and reduce the concentration of PCDD/Fs in the flue gases and fly ashes. The dominant formation pathway of the PCDD/Fs in this study is de novo synthesis. Chlorine induced by SMSW is the main factor influencing the concentration of the PCDD/Fs in both flue gas and fly ashes. These findings are helpful for the further development of co-combustion with renewable energy in coal-fired incinerators, yet more investigation on PCDD/Fs is still required to be conducted in the future.