The invention discloses a beta titanium alloy and a preparation method thereof, relates to a titanium alloy, and provides a beta titanium alloy with excellent combination property and a preparation method thereof. The beta titanium alloy comprises the following components by mass percent: 6-10% of vanadium, 2-4% of aluminum, 2-4% of chromium, 0-13% of niobium, 0-3% of tin, 0-5% of zirconium, 0-4% of molybdenum, 0-0.05% of boron and the balance titanium. The preparation method comprises the following steps: putting the titanium and zirconium in a sponge state into an arc furnace; vacuumizing and then charging argon for smelting; smelting the smelted titanium and zirconium with vanadium, aluminum, chromium, niobium, tin, molybdenum and boron to obtain a beta titanium alloy pig material; carrying out homogenizing heat treatment on the beta titanium alloy pig material, and cooling along with the furnace; rolling the beta titanium alloy pig material after the heat treatment into a schistose alloy material; slicing the obtained schistose alloy material into a sample; and quenching with icy water after the solution treatment, and then carrying out aging to obtain the beta titanium alloy.