Abstract: The 600 MW fast reactor drive shaft made of FXM-19 material is characterized by a large overall dimension (6700 mm in length), complex evolution of high-temperature diffusion precipitates, and difficult control of forged grain structure homogeneity. Through experiments and analysis, the evolution laws of high-temperature diffusion precipitates and the grain structure evolution during the forging heating process are systematically studied. A two-stage heating method (low-temperature long-time + high-temperature short-time) and compatible forging and solution treatment processes are designed. They are based on the different stored energy states of internal and external grains after cogging. Through product manufacturing and testing, the two-stage heating and forging-solution process is verified to effectively control the grain structure and mechanical properties. For the manufactured products, a room-temperature yield strength of ≥442 MPa, an ultimate tensile strength of ≥795 MPa, and an elongation after fracture (A) of ≥48.4% are achieved, and the grain size is controlled at grade 4-5. This indicates that the process scheme formulated based on grain stored energy analysis is highly reliable for the prediction of microstructure and property control. The research results are considered to be of great significance to the hot working and manufacturing of large FXM-19 forgings.