The invention discloses a method for preparing a fine-grain high-density TZM (Titanium-Zirconium-Molybdenum Allo) alloy. The method disclosed by the invention comprises the following steps of: with pure molybdenum powder, ZrH2 powder, La2O3 powder and graphite powder as raw materials, mixing the raw materials, and carrying out ball milling, press molding, presintering and high-temperature sintering to obtain the TZM alloy. The TZM alloy prepared by using the method disclosed by the invention has the characteristics of fine crystal grains, distribution uniformity, low porosity, high compactness, simple preparation process and strong operability and controllability and has the most remarkable advantages that: on the basis of the traditional ZTM alloy preparation method, rare earth oxide La2O3 is solid-solid doped in the alloy powders, a mode of combining mixing and ball-milling of the alloy powders and a mode of sectional sintering during high-temperature sintering are adopted, crystal grains are fined, the alloy density is remarkably improved, the sintering temperature of the TZM alloy is reduced to 1800-2000 DEG C from 2100-2300 DEG C in the traditional method, therefore energy resources are saved and requirements of an enterprise on the fine-grain TZM alloy material with high density can be met.