The invention provides a fire mold investment cast casting method applied to the technical field of casting technologies. The fire mold investment cast casting method includes the casting steps that 1, graphite sand is smeared on the outer surfaces of core bulges (3) and the inner surfaces of shell bulges (4); 2, a core (1) is installed in a shell (2) in a sleeved mode, and a cavity (7) is formed between the core (1) and the shell (2); 3, the shell (2) is heated, the heated shell (2) is put into cold water for hardening, and a cast machining solution is poured into the cavity (7) between the hardened shell (2) and the core (1). According to the fire mold investment cast casting method, the steps are simple, aiming at the defect of shrinkage likely to happen on the thin parts of the wall of a cast, shrinkage is effectively solved, the thickness of the thin-wall parts is increased, and the defect of cold shutting is also eliminated on the thin-wall parts, so that the total quality of the cast is effectively improved, while the casting technology is simplified, and the casting cost is lowered.