Abstract: Two typical flaws were found in both heavy and medium plate by means of ultrasonic flaw detection. Utilizing macroscopic examination and metallographic examination combining with the distribution of these flaws in the plate, the forming reason of the flaws was investigated. The results show that the cluster flaws were related to the center segregation in the continuous casting billet. Stripy flaws on the narrow side of the plate derived from the cracks within the triangular zone or central cracks close to the triangular zone. Furthermore, stripy flaws inside the steel plate mainly resulted from the intermediate cracks.