Abstract: Nuclear-grade 316H austenitic stainless steel has extremely high requirements for microstructural uniformity and magnetic properties, and the ferrite magnetic phase in its structure must be strictly controlled. In this paper, the variations of ferrite morphology, content, precipitate characteristics, and solidification mode from the surface to the center of a 316H austenitic stainless steel electroslag ingot were investigated using metallographic microscopy, scanning electron microscopy (SEM), energydispersive xray spectroscopy (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and ThermoCalc thermodynamic calculations. The results show that from the surface to the center of the electroslag ingot, the cooling rate gradually decreases from 1.22 °C/s to 0.24 °C/s, and the ferrite morphology evolves successively from granular to short rod-like, and then to skeletal and network-like, while the secondary dendrite arm spacing increases. The ferrite content ranges from 1.92% to 3.57%, exhibiting an “M”-shaped distribution; the high cooling rate at the surface suppresses ferrite formation, while at the center, the decomposition of ferrite under the FA solidification mode leads to a decrease in content. From the edge to the center, the solidification mode changes from AF mode to FA mode, whereas the Thermo-Calc thermodynamic equilibrium solidification result indicates the FA mode. Regarding precipitates, secondary precipitates at the edge of the ingot are formed at ferrite grain boundaries, whereas those at the center are mostly located inside ferrite grains. At the edge, ferrite decomposes directly at grain boundaries to form sigma phase and chi phase; at the center, ferrite primarily transforms through a eutectoid reaction to form sigma phase and γⅡ (secondary austenite), with no chi phase observed at the center. At both the edge and center positions, Cr-rich regions on ferrite promote the formation of Cr??C? carbides.