Experiments were performed to investigate the release behavior of potassium and sodium in the biomass high-temperature entrained-flow gasification with the addition of acid oxide SiO2, basic oxide MgO, amphoteric oxide Al2O3. The results showed that the volatilization of alkali was found to strongly depend on temperature. High gasification temperature strengthened the alkali release. When the reactor temperature was 1200°C, the volatilization of alkali species were about 37.87% for K and 71.14% for Na. Three additives all favored the retention of potassium and sodium and the content of water-soluble potassium and sodium in the ash. Among the three additives, MgO had the best retention effect. The potassium and sodium content in the gas phase was as low as 46.6% and 67.3% compared with raw straw, respectively. In the entrained-flow gasification with short residence time, the additives retained more alkali metals by the physical and chemical adsorption. Part of the additive utilized as physical adsorbent during the gasification enhanced the ash melting point of the residue carbon.