The invention relates to a precision casting method for titanium master alloy by means of casting die bottom-drain vacuum suction casting, belonging to the technical field of precision casting methods for titanium master alloy. The precision casting method in the invention solves the problems in the prior processing technique for titanium master alloy, such as large workload, higher process costs, complex preparation processes, the liability of the alloy to the pollution of interstitial elements during the preparation procedure, poor compactness, and bad quality of the castings. The precision casting method comprises the following steps: making the casting die; conducting vacuum melting of the alloy in a non-consumable electrode arc furnace; turning over the melted titanium mater alloy into a suction casting crucible for remelting and keeping a certain degree of superheat; vacuumizing a vacuum chamber where the casting die is arranged, opening the suction casting button on the suction casting crucible, and enabling the liquid titanium master alloy to fill up the casting die under the actions of the self-gravity and pressure difference, thus obtaining the required casting member. The titanium master alloy casting member produced by the precision casting method in the invention has the advantages of full die filling, good surface quality, fine grains of the casting structure sized from 10 to 30 Mu m, correspondingly thinned dendritic crystal, less segregation, and compact structure.