Abstract: High-temperature thermoplasticity tests were conducted on large-scale H13 steel continuous casting billets with diameters exceeding 120 mm within the temperature range of 600–1 300 ℃ with a Gleeble-3800 thermal simulator. The high-temperature thermoplasticity was investigated, and the fracture morphology and microstructure near the fracture were observed to analyze the fracture mechanism. The results show that with increasing temperature, the tensile strength of H13 steel continuous casting billets continuously decreased, and the percentage reduction of area decreased, then increased, and decreased. The“pocket”brittle zone formed by the connection of the medium-temperature brittle zone and the low-temperature brittle zone had a wide range, ranging from 600 ℃ to 1 150 ℃; the fracture mode was intergranular fracture and quasi-cleavage fracture, and there were grain boundary cracks near the fracture. The high-temperature thermoplasticity zone range was narrow, ranging from 1 150 ℃ to 1 250 ℃, where the percentage reduction of area exceeded 60% and the main fracture mode was ductile fracture without significant cracks in the microstructure near the fracture. The narrow range for high-temperature thermoplasticity zone of H13 steel indicated that the controllable temperature range in its continuous casting and hot rolling processes was narrow, and the on-site production had high requirements for temperature control.