Constrained groove pressing (CGP) is a modern process for the formation of ultrafine grain in metallic sheets with high mechanical properties. During CGP, the sheet metal are subjected to repetitive corrugating and straightening under the plane strain deformation condition by utilizing alternate pressing with the asymmetrically grooved dies and flat dies. This leads to an increase in the degree of plastic strain of the sheet metal without changing its original dimensions. CGP can effectively refine the grain structure to a sub-micron level. Materials processed by CGP have a very high strength, high hardness and many other required properties. This review focuses mainly on CGP process technology, especially the number of passes, as well as the study of microstructure changes. Most of the scientific results were obtained experimentally.