Abstract: In-situ research was conducted to illuminate the high-temperature behavior of primary carbide in H13 steel that had been cast in different ways. Experimental observations indicate the obvious segregation of Cr, Mo, V, and C in the interdendrite zone of continuously cast and electroslag remelting (ESR) samples. In the interdendrite zone, primary carbide is composed of Cr, Mo, V, and Ti. A liquid phase was observed to occur around the primary carbide of two as-cast samples cast by continuous casting and ESR processes when heated to 1200℃ and 1250℃, respectively. The temperature at which the liquid phase appears agrees well with theoretical calculations. The liquid-phase region expands as the heating temperature increases and the continuous casting sample shows a larger liquid zone. The emergence of a partial liquid phase accelerates the diffusion of the segregated elements and is an important factor in the high-temperature behavior of primary carbide.