To accurately describe the heat transfer and melting characteristics of a calcium‐cored wire in molten steel, the finite difference method is used in theoretical calculations to solve the relationship between the melting temperature, radius, and time. Numerical simulations are performed using the Eulerian–Eulerian method to characterize the temperature distribution at different periods. The results show that the radius of the calcium wire and steel shell both decrease and the melting rate gradually increases. The calcium‐cored wire has a fish‐scale temperature distribution, with the temperature decreasing from a maximum at the front down to the tail end and increasing outward from the center axis. The temperature of the wire core is 1120 K at 0.272 s, indicating the complete melting of the pure internal calcium. The temperature of the calcium wire–steel shell interface reaches 1793 K at 0.979 s and remains from 1645 to 1757 K at the front of calcium wire. The steel shell melts through, and calcium flows into the molten steel in liquid form. The numerical simulation results generally agree with the theoretical calculations, and the reliability of the model is verified by comparison with published studies.