Incineration is widely used as the mainstream way to achieve the rapid reduction and harmless disposal of sludge in China,and with the aim of "double carbon" emission reduction plan,co-combustion of sludge with coal can realize the carbon emission reduction and the clean incineration of sludge. However,there are still many problems in slagging,combustion pollutant emission and technical economy. The basic physical and chemical characteristics,water content distribution,coal quality index,and drying technologies of sludge were analyzed. The advantages and disadvantages of three technical routes of co-combustion of sludge with coal,i.e.,direct co-combustion,co-combustion of sludge dried directly by flue gas,and co-combustion of sludge dried indirectly by steam,were thoroughly analyzed based on the typical co-combustion projects. The results show that direct co-combustion of wet sludge is faced with poor combustion stability and low disposal capacity,and the combination of drying and co-combustion can achieve a large disposal capacity and ensure the combustion stability. Considering the problems of high dust explosion risk and large demand for flue gas in the direct drying of sludge by flue gas,co-combustion of sludge dried indirectly by steam is a better choice with good combustion performance. Among sludge indirect-drying technologies,paddle drying and rotary disc drying have high thermal efficiency,low dust production,and small floor area. Due to the existence of viscosity during sludge drying,it is necessary to select an appropriate drying model to analyze the heat and mass transfer process. Based on the operation practice of typical co-combustion projects in China,it is found that when the blending ratio of sludge is well controlled,co-combustion technology can not only ensure high combustion thermal efficiency,but also meet the emission standards of pollutants including conventional pollutants,heavy metals and dioxins. In terms of national policy,it is urgent to clarify and refine corresponding policies,e.g.,the pollutant emission standard,power generation subsidy standard,and carbon emission reduction accounting standard,to promote the development of co-combustion of sludge with coal.