The invention relates to a preparation method of beta-aluminum fluoride with high specific surface area. Against for the defects of the prior art for preparing the aluminum fluoride with high specific surface area that the preparation process is complicated, the preparation period is long, the operation and the control are difficult, and the corrosion on the device is large, the invention provides a preparation method of beta-aluminum fluoride with high specific surface area with simple preparation process, short preparation period, easy operation and control and small corrosion on the device. The invention adopts the technical scheme that: gamma-alumina, carbon source and HF gas are adopted as raw materials, water solution of carbon source is soaked into the gamma-alumina in an equivalent soaking method, the gamma-alumina after being soaked with the carbon source is dried and carbonized to obtain gamma-alumina containing carbon, then the gamma-alumina containing the carbon is reactedwith HF gas to obtain the aluminum fluoride containing carbon, and finally the aluminum fluoride containing the carbon is decarbonized, acidified, washed, dried and roasted to obtain the beta-aluminum fluoride with high specific surface area.