To mitigate increasing environmental pressures, biomass is becoming a crucial alternative energy source worldwide. Ash fusion characteristics of biomass has closely related to ash-related problems during its conversion. The fusion characteristics of cotton stalk (CS), the deposition from CS vibrating grate furnace combustion (DCS), and their modification mechanisms were investigated. The results indicate the sintering temperature (Ts) and ash fusion temperature (AFT) of DCS are lower than that of CS. Kaolinite causes obvious increases in the Ts and flow temperature, while the additions of calcite and Ca-sludge waste (Ca-W) make Dcs deformation temperature increase more obviously than that of flow temperature. That an increase in kalsilite content and leucite formation make the mixture Ts and AFT increase with increasing kaolinite proportion; the replacement of K+ in the silicates by Ca2+ causes the formations of high melting point Ca2+ silicates (e.g., rankinite and wollastonite) with increasing calcite or Ca-W, which makes their Ts and AFT increase. It is found that the deformation temperature corresponds to the temperature at which its liquid phase content at 15% or so based on FactSage calculation.