The testing device self-designed was used to measure the shrinkage ratio of Fe-0.18%C alloy in the length direction of cast ingot with the dimension of 200×80×100 mm. The results show that the total linear shrinkage mass of cast ingot is 0.0281 mm in the range of 4 mm near the inner surface of water-cooled crystallizer from the beginning of solidification to the end of δ→γ transformation. The shrinkage mass of δ phase and δ→γ transformation is 0.0211 mm and 0.007 mm, which is 75% and 25% of total shrinkage mass, respectively. The shrinkage rate of δ phase and δ→γ transformation is 0.45 μm·s-1 and 1.45 μm·s-1, respectively. The shrinkage mass in the cross section of cast ingot is less than the free shrinkage mass observed by using a confocal laser scanning microscope.