Abstract: Co-gasification of agroforestry waste biomass and coal realizes energy-saving, low-carbon emission, clean and efficient raw material conversion by taking advantage of their similarities and complementarities. The physicochemical properties of ash slag for raw materials are one of the key factors affecting the stable operation of co-gasification. It is the focus of co-gasification research. This paper reviews the research status of physicochemical properties of ash slag from co-gasification of agroforestry waste biomass and coal. It mainly includes the similarity and difference between agroforestry waste biomass ash and coal ash, the fusion and viscosity-temperature characteristics of mixed ash, the effect of alkali/alkaline earth metals in mixed ash on co-gasification reactivity, and sintering behavior during the slagging process. The influence mechanism of adding agroforestry waste biomass on the melting flow and sintering behavior of mixed ash is discussed. The prediction models and methods of fusion characteristics, viscosity-temperature, and slagging characteristics of mixed ash are also summarized. Finally, the future research directions of ash slag from co-gasification of agroforestry waste biomass and coal are proposed.