Disclosed is a biomedical β titanium alloy and a preparation method thereof. Its composition includes: Mo: 9.20-13.50%; Fe: 1.00-3.20%; Zr: 3.50-8.20%; Ta: 0-1.00%; the balance is Ti. The β titanium alloy is suitable for the laser additive manufacturing technology, and the prepared parts have a dense equiaxed grain structure with ultra-low grain size and a small number of columnar grain structures, which produces a fine-grain strengthening effect, and greatly improve the hardness and tribocorrosion performance of the alloy material. Also provided is a method for preparing a non-toxic, low-elasticity, and tribocorrosion resistant biomedical β titanium alloy material. A powder prepared from the above alloy components is subjected to a laser additive manufacturing technology to prepare a corresponding β titanium alloy with high-hardness, good tribocorrosion resistance and extremely low cytotoxicity. Moreover, the prepared material has good weldability and is a special metal alloy powder suitable for laser additive manufacturing.