The present invention relates to a display technique which can clearly display billet section frozen structure image and do not pollute environment, and includes the following steps: 1. sampling and preparation; 2. etching sample; 3. image processing and making picture, adopting digital camera or scanner and utilizing computer to make image processing of cast billet frozen structure. Said invention can quickly provide complete clear cast billet frozen structure image, and measure the data of ratio of columnar crystal and equiaxial crystal, grain fineness, etc. so as to provide reliable basis for evaluating internal quality of cast boillet.