Abstract: As a renewable and clean energy,biomass will play an increasingly important role in Chinese energy structure.The content of alkali metal elements( mainly K) in biomass is usually relatively rich,and it is the main component of biomass ash.Alkali metals in biomass are easily released in combustion due to the low melting point of alkali metal inorganic salts( for example,KCl),which brings serious technical safety problems to the development and utilization of biomass energy. In the biomass combustion process,partial alkali metal ash is easy to condense,adsorb and deposit on the heated surface of the boiler chamber after the gaseous release,which causes problems such as pollution,scale formation and ash accumulation and seriously affects the heat transfer of the boiler and even causes corrosion.Therefore,the release law and mechanism of alkali metal elements in the process of biomass combustion research will provide strong theoretical support for the clean and efficient utilization of biomass in China,which has good socio-economic and academic significance.In this paper,the release characteristics of alkali metals in the biomass combustion process of wheat straw were studied. The release characteristics of alkali metals at the combustion temperature of 400-900 ℃ were researched through the horizontal tube furnace and XRD,SEM-EDS and other test means.The results show that alkali metal K mainly exists in the form of water soluble,while alkali earth metals Ca and Mg mainly exists in the form of ammonium acetate soluble and water soluble.Water-soluble K mainly exists in hydrated ions or crystals of KCl,KNO_3,K_2SO_4 and K_3PO_4.In the combustion process,the main organic K and a small amount of inorganic K release within 400 ℃,inorganic potassium in the form of KNO_3 is mainly released within 400-600 ℃,KCl and KNO_3 are mainly released above 600 ℃.Alkaline earth metals Ca and Mg form relatively stable compounds which are not easy to release.K and Cl contents change synchronously according to the analysis of element enrichment on the ash surface,.K and Cl contents grow simultaneously below 600 ℃ mainly because there are more alkali metal compounds in the form of KCl.K and Cl contents on the surface of ash surface reduce over 600 ℃ mainly because KCl reacts with SiO_2,or directly release in the form of KCl.