Based on the fact that the compositions of chrysotile asbestos tailings are mainly SiO₂ and MgO, the authors efficiently extracted MgO from chrysotile asbestos tailings with ammonium bisulfate via mix-roasting, and investigated the interrelationships between MgO extracting rate, washing mix-roasting residue and phase so as to get the optimal mix-roasting parameters. According to the physical phase variation of the washing mix-roasting residues, the authors analyzed the change of minerals and products in the mix-roasting process. The result shows that the optimum conditions for the elimination of mental oxides in mix-roasting were 4 for NH₄HSO₄/MgO molar ratio, 500℃ for the roasting temperature, 2 h for the roasting time, and 120 mesh for the particle size. Brucite, calcite and kotschubeite were most reactive in the mix-roasting process, followed by serpentite and then by talc. The mental oxides in chrysotile asbestos tailings were changed into soluble sulfate after being reacted with ammonium bisulfate. Meanwhile, Si-O tetrahedral sheet was retained and modified, and finally active silica residue was preserved. The results obtained by the authors have an important significance for the efficient utilization of chrysotile asbestos tailings.