Abstract: Hydrothermal carbonization（HTC）experiments of rice straw were carried out. The releasing behavior of the alkali and alkaline earth metals（AAEMs）were investigated using inductively coupled plasma optical emission spectrometry analysis,and calculation of slagging and fouling indices. The results indicate that the hydrochar yield gradually decreases from 60.8% to 35.6%,while the liquid product yield increases from 32% to 53.2% with reaction severity increasing from 3.85 to 8.27. If the carbonization for hydrothermal reaction of rice straw is expected,the severity should be below 6.5. The residual rate of AAEMs decreases when the reaction severity increases. As the severity approaches to 8.27,the residual rate of K and Na is 3.6% and 6.6%,respectively. And the lowest residual rate of Mg and Ca is 49.7% and 77.1%,respectively. At the same time,the residual rate of Si increases from 68.8% to74.6% with increase of reaction severity. However,the residual rate of the ash of the rice straw hydrochar increases first and then decreases,which is 66.76% when the severity is 8.27. The slagging and fouling indices calculated are lower than the reference values.The processing of HTC improves the slagging and fouling behavior of rice straw hydrochar.