Abstract: To tackle the problems related to casting of the Φ720 mm plug used by the tube expanding mill like scabbing and hard conditioning,numerous technological optimizations and improvements on the actual manufacturing process are conducted. As a result,a rather rational solution of the casting process for the finishing plug of the expanding mill is made to enhance the finished product yield. Relevant operation result shows that using the limestone sand to make the core for heavy-wall cast can eliminate the above mentioned two problems.