The 320 mm defective continuous casting slab is provided from the domestic factory， and the sample size is 160 mm × 100 mm× 180 mm. It is rolled in laboratory with simulation ratio being 2.0. The samples are divided into three groups ac- cording to the average reduction. Each group are rolled into three different thickness plates. The average reduction corresponds to the critical reduction， which is rough rolling passes to meet the dynamic geometry（ l/h =0.53）. The detection test shows that the defects of all the samples after rolling have been pressed together， verified the critical condition of defects lamination.