The invention discloses a tungsten alloy powder casting machining method. The method comprises the steps that S1, spherical tungsten powder is prepared; S2, mixed tungsten alloy powder is prepared; S3, injection molding is conducted, specifically, the mixed tungsten alloy powder and an adhesive are mixed and then made into granules, and then the granules are fed into an injection molding machine to be subjected to injection molding in a mold to obtain a tungsten alloy blank; S4, solvent degreasing is conducted, specifically, the tungsten alloy blank is put into a normal-temperature n-heptane solvent to be soaked for 6-10 hours and then dried for standby application; and S5, thermal degreasing is conducted, specifically, the tungsten alloy blank obtained after solvent degreasing is buried in Al2O3 powder to be subjected to segmented thermal degreasing, and is slowly cooled to the normal temperature to obtain an ultrahigh-density tungsten alloy powder casting. According to the method, tungsten alloy parts with ultrahigh density and ultrahigh shape complexity can be directly prepared, and the problems that in the prior art, machining is complex, energy consumption is large, the manufacturing cost is high, raw material waste is large, and the rate of finished products is extremely low are solved.