Abstract: The application of liquid core reduction (LCR) technology in thin slab continuous casting can refine the internal microstructures of slabs and improve their production efficiency. To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments, the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined. With SPA-H weathering steel as a specific research steel grade, the distributions of temperature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal–mechanical finite element model. High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures, and a prediction model of the critical strain for two typical cracks, combining the effects of strain rate and temperature, was proposed by incorporating the Zener–Hollomon parameter. The crack risks with different LCR schemes were calculated using the crack risk prediction model, and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm × 1600 mm was 41.8 mm, with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8, 7.3, 6.5, 6.4, and 5.8 mm, respectively.