The invention relates to the technical field of metallurgy, and particularly relates to a method for determining solidification shape and dimensions at a specific position of a plate blank. The methoddisclosed by the invention comprises the following steps: gradually pressing a casting blank, and counting pressure change; determining a critical pressing state; treating the cross section of the casting blank; preparing compactness grids and standard compactness, drawing up a contour line, and the like. The method disclosed by the invention is used for measuring the shape and the dimensions ofan unsolidified area, and has the advantages of being accurate in measurement value, low in measurement cost, easy to implement, and the like, so that measurement for the solidification shape and dimensions of the casting blank at the specific position of the plate blank becomes possible, and basis is provided for process analysis under single-roll great pressing.