Heat transfer behavior of a steel ladle filled with molten steel is comprehensively analyzed for subsequent design of the matched thermoelectric devices. Considering the influence of the flow and thermal stratification of molten steel on heat dissipation, a mathematical model that describes both the inner transient flow and heat transfer of molten steel and the outer heat dissipation of ladle wall and slag is established. An innovative two-step method is applied to make the simulation accord with actual industrial process. The results show the non-uniform temperature and natural convection of molten steel has a significant effect on the heat transfer of wall and slag but a weak effect on temperature variation and heat dissipation of the surfaces. The steel ladle can be considered as a steady heat source. Moreover, the heat loss of sidewall is the main path of ladle's and accounts for more than half of the total. Besides, radiation is the main form of heat dissipation. The surface temperature distribution in the vertical direction of the sidewall has a large difference. However, the region of sidewall surface under slag line is with a high and relatively uniform temperature and is conducive to the stability of thermoelectric conversion. Finally, a primary solution of waste-heat utilization of steel ladle is proposed.