To provide a technique capable of simply evaluating whether or not mold powder can suppress the formation of a slag bear without measuring compressive strength.

Mold powder M packed into a crucible 2 is heated for 10 to 30 min under the heating conditions where its temperature gradient lies in a prescribed temperature gradient G [°C/mm] within the range of 2 to 30, and the temperature distribution along the direction of the above temperature gradient G [°C/min] at least includes a temperature range ΔT[°C] of 400 to 1,300. The thickness D[mm] of the sintered layer formed by the heating is measured. In the case inequality (1) is satisfied, it is evaluated that the mold powder M can suppress the formation of a slag bear by the system.