Release and reactions of elements in biomass ash of rice straw, corn cob, palm kernel shell and wheat straw enzymatic hydrolysis residue were investigated by experiments of biomass ash sintering and melting. The ash was considered to be sintering as the Mohs’ scale of hardness was up to 3, which would block the burner or gasifier. The ash in this paper was prepared at 600℃, and put into the tubular furnace of 700~1200℃ in order to evaluate the temperature of sintering and melting. The ash was put into the tubular furnace at the sintering temperature for 5~30min, which showed the process of sintering. According to the analysis of ash by XRF and XRD, volatilization of KCl became obvious after 800℃. Parts of K and Na stayed in the ash, forming alkali feldspars in the reactions with SiO2 and Al2O3. Volatilization of alkali metals would cause an increase of melting temperature in TG-DSC and fusion test, which is different from the character of coal ash. The method of evaluating the coal ash sintering temperature is unreliable for the ash of biomass. Different elements in the ash have different characteristics of melting and reactions, which decides the sintering temperature. The sintering temperature decreases with more Al, Ca, K, Na, S or less Mg, Fe, P, while the influence of Si is weak. As the main composition of biomass ash is SiO2, the sintering temperature can be estimated to be 0.9 times of sintering temperature. Using the data of four kinds of biomass ash in the experiment, the linear regression fits for the sintering temperature against the mass percentage of ash components was obtained with R2 of 0.967 and error of 25.6℃ for the sintering temperature range of 950~1200℃.