In order to improve the properties of purging plugs and to prolong their service life, this work attempted to impregnate alumina-spinel castables for purging plugs in refining ladle with saturated magnesium chloride solution under vacuum. After being impregnated for the first time, the specimens were treated in two different ways: (1) dried at 110 ℃ for 24 h; (2) heated at 600 ℃ for 3 h. Then they were impregnated for the second time. All specimens were heated at 1 550 ℃ for 3 h, then the cold properties and the high temperature properties were tested according to corresponding standards. Test results were compared and analyzed. The results show that: after being impregnated, the specimen have both better cold properties and high temperature properties, the microstructure analysis result proves that it is attributed to in situ formed spinel. However, because MgO produced by MgCl2 · 6H2O decomposing above 527 ℃ can hydrate and destroy specimen microstructure, which can make the properties of specimens impregnated in the second way get worse. By comprehensive consideration, the first scheme way is more suitable.