The surface cracks might appear on continuous casting slab, whose evolution behavior during hot rolling severely affects the quality of rolled products. The behavior of surface cracks during rolling was simulated by thermal-mechanical finite element method. The shape of crack, the stress field distribution and the temperature field distribution around the crack in the deformation zone during rolling were obtained. Results show that the cracks gradually close in the entry position, but which gradually open again in the exit zone of the deformation zone. And the tension stress appears around the crack tip in the exit position. Meanwhile, the phenomenon of two peaks of temperature on crack tip in the deformation zone is discovered.