The invention discloses a shaping tool for large blade heat treatment. Large blades of a steam turbine can generate deformation and internal stress in machining of air way molded lines and welding ofStellite alloy sheets, so that the quality requirements of the blades are difficult to meet, no working allowance caused by appearance of steam ways in the blades in finishing is generated, the rebound caused by internal stress in the blades in blade assembly is generated, and the blade crown assembly requirements cannot be met in blade assembly. Blade crown parts of the large blades are ejected against blade crown thimble bases; molded line segments of the large blades are matched with molded line positioning bases; air way molded line segments of the large blades are arranged on L-gear molded line positioning blocks; blade root parts of the large blades are clamped on blade root positioning bases; and molded line positioning end surfaces matched with tiepiece molded line segments of thelarge blades are formed among A# molded line pressing end surfaces, B# molded line pressing end surfaces, C# molded line pressing end surfaces, D# molded line pressing end surfaces, G# molded line pressing end surfaces, J# molded line pressing end surfaces and split positioning end surfaces. The shaping tool for large blade heat treatment is used for positioning the large blades.