In this paper, combined with experiments and theoretical calculations, the effect of urban low-calorific value sludge on the slagging characteristics of easy-slagging coals is studied. The results show that when the melting point of sludge ash is lower than that of coal ash, the ash melting point of the mixture after the two blends will be lower than the melting point of raw coal ash. When SiO2 and Al2O3, which are relatively high in sludge, are used as single additives, the ash melting point of coal will first decrease and then increase. As the mixing ratio of sludge increases, coal ash slagging characteristics show a trend of gradual relief. For coals that are prone to slagging and rich in alkali metals, they can be appropriately mixed with sludge rich in silicon and aluminum compounds or additives to improve Slagging characteristics.