The invention discloses a Beta titanium alloy used for a fastener. The Beta titanium alloy comprises the following components, in weight percentage: molybdenum: 4 to 7 percent, niobium: 4 to 6.5 percent, chromium: 3 to 5 percent, tantalum: 1 to 3 percent, aluminum: 2 to 4 percent, iron: 1.0 percent or less, carbon: 0.1 percent or less, nitrogen: 0.05 percent or less, hydrogen: 0.015 percent or less, oxygen: 0.02 percent or less, balance titanium. A preparation method thereof is characterized in that after sponge titanium, pure aluminum, pure chromium, Ti-0.31Mo, Ti-0.53Nb and Al-0.80Ta are mixed and pressed with a pressing machine into block-shaped electrodes; a plurality of electrodes are welded with an ion welding machine into a long strip-shaped electrode which is taken as a consumable electrode and melted in a vacuum consumable arc furnace, the obtained casting ingot is again taken as the consumable electrode and melted for 2 to 3 times to acquire the product titanium alloy ingot. The invention has the advantages that the intensity is high, the low-cost large-scale production can be realized, the intensity requirements can be satisfied, the processing and modeling are easy, and the energy consumption is reduced.