To provide a method for predicting and detecting surface defect, with which sign of the surface defect caused in a mold during casting is accurately predicted not only at positions where a temp. measuring element is set, but also at the other position in the mold plane in on-line and the surface defect on the surface can be reduced to the lowest minimum.

In the mold for continuous casting, plural temp. measuring elements are set in the casting direction and/or in the width direction, to measure the mold temp. and at the same time, the heat transfer and solidification calculation is executed in the on-line from the measured molten steel surface level and casting speed to calculate the shell thickness of a cast slab and the temp. distribution in the shell. Based on these values, the deformation and the stress state of the cast slab in the casting direction and the peripheral direction of the mold are calculated, and when tension stress value or strain becomes a prescribed value, the occurrence of the surface flaw in the cast slab is detected or predicted.