Abstract: To investigate the effect of potassium migration on the hydrothermal carbonization of biomass,de-ashing millet stalk was saltimpregnated with KCl and HCOOK respectively. The hydrothermal carbonization experiments of untreated and pretreated millet stalk were carried out. The characteristics of the hydrochar prepared was analyzed. The results show that the hydrochar yield of the de-ashing millet stalk loaded with HCOOK decreases from 65.1% to 20.0% at 150-300 ℃ for 240 min,which are lower than those of the hydrochars obtained from millet stalk. However,when the temperature is higher than 240 ℃,the hydrochar yield of the de-ashing millet stalk loaded with KCl is different from those of the former,and gradually approaches the hydrochar yield of the millet stalk. The carbon content of the hydrochars of the salt-impregnated millet stalk is slightly higher than that of the millet stalk hydrochar at 210 ℃,but it is opposite at 300 ℃. The specific surface area of the hydrochar of de-ashing millet stalk loaded with KCl increases with the increase of temperature and is significantly higher than that of raw millet stalk. However,at 300 ℃,the specific surface area of the hydrochar of deashing millet stalk loaded with HCOOK is 0.69 m~2/g,which is lower than that of raw millet stalk. KCl can promote the reaction of hydrothermal carbonization and develop the pore structure of hydrochar from millet stalk,while HCOOK presents the opposite effect.