The whisker MgSO4·5Mg（OH）2·3H2O（MOS）was prepared by the hydrothermal method at 170℃ for 6 h，after NaOH solution and MgSO4 solution with a specific concentration reacting in a rotor-stator reactor. The effects of preparation equipment of intermediate product，reactant concentration and rotor speed on the product quality were discussed and the process conditions for the preparation of MOS by the rotor-stator reactor and the hydrothermal method were determined. Under the same conditions，good quality MOS was also prepared in a pilot test in 100 L autoclave. The whisker produced by this method was more than 50 in aspect ratio and 0.5—1.0 μm in diameter，with smooth surface and high dispersibility.