Abstract: <SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: " 宋体? mso-fareast-font-family: AR-SA; mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: 12.0pt; mso-bidi-font-size: Roman?; New Times>Anhydration and thermal decomposition processes of magnesium sulfate made from magnesium chloride were studied by TG-DSC and XRD.Effects of factors,such as thermal decomposition temperature,time,and particle diameter,on resolution ratio of decomposition from anhydrous magnesium sulfate to magnesia were mainly investigated.Experiments showed that anhydration process of magnesium sulfate heptahydrate was completed between 60~300 </SPAN><SPAN style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: " mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: Roman?; New Times AR-SA? ?Times mso-bidi-font-family: mso-hansi-font-family:>℃</SPAN><SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: " 宋体? mso-fareast-font-family: AR-SA; mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: 12.0pt; mso-bidi-font-size: Roman?; New Times> and thermal decomposition of anhydrous magnesium sulfate was completed between 950~1 150 </SPAN><SPAN style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: " mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: Roman?; New Times AR-SA? ?Times mso-bidi-font-family: mso-hansi-font-family:>℃</SPAN><SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: " 宋体? mso-fareast-font-family: AR-SA; mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: 12.0pt; mso-bidi-font-size: Roman?; New Times>.Magnesia with high purity was gained by direct decomposition of anhydrous magnesium sulfate through controlling experiment conditions of solid phase and separating the anhydration and thermal decomposition.Orthogonal experiment was used to optimize the process conditions.High purity magnesia with cubic crystal structure and mass fraction of 99.8% can be obtained from magnesium sulfate heptahydrate (particle size of 109 </SPAN><SPAN style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: " mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: Roman?; New Times AR-SA? ?Times mso-bidi-font-family: mso-hansi-font-family:>μ</SPAN><SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: " 宋体? mso-fareast-font-family: AR-SA; mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: 12.0pt; mso-bidi-font-size: Roman?; New Times>m) under the condition as follows</SPAN><SPAN style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: " mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: Roman?; New Times AR-SA? ?Times mso-bidi-font-family: mso-hansi-font-family:>：</SPAN><SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: " 宋体? mso-fareast-font-family: AR-SA; mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: 12.0pt; mso-bidi-font-size: Roman?; New Times>dehydrating for 0.5 h under 400 </SPAN><SPAN style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: " mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: Roman?; New Times AR-SA? ?Times mso-bidi-font-family: mso-hansi-font-family:>℃</SPAN><SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: " 宋体? mso-fareast-font-family: AR-SA; mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: 12.0pt; mso-bidi-font-size: Roman?; New Times>,and homothermal disintegrating 1 h under 1 100 </SPAN><SPAN style="FONT-SIZE: 10.5pt; FONT-FAMILY: 宋体; mso-bidi-font-size: 12.0pt; mso-ascii-font-family: " mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: Roman?; New Times AR-SA? ?Times mso-bidi-font-family: mso-hansi-font-family:>℃</SPAN><SPAN lang=EN-US style="FONT-SIZE: 10.5pt; FONT-FAMILY: " 宋体? mso-fareast-font-family: AR-SA; mso-bidi-language: ZH-CN; mso-fareast-language: EN-US; mso-ansi-language: 1.0pt; mso-font-kerning: 12.0pt; mso-bidi-font-size: Roman?; New Times> in crucible resistance furnace. </SPAN>