Abstract: Elaborated in the essay are the history and the main technical parameters of the 4-roll hot-sizing mill. Also described are the groove design tips and the technical characteristics of such aspects of the mill, in- cluding the structure of the mill, design of the roll length, roll drive type and method for roll clearance elimination, etc. Furthermore, a brief discussion is made on the proportional relationship of groove radius difference of the three sizing mill types, i.e., the 2-roll type, the 3-roll type and the 4-roll type. Statistical analysis of the OD measurement data of the products with typical sizes is conducted. Based on the analysis result, periodical production experience is summarized, and the general evaluation of and relevant suggestions for the 4-roll hot-sizing mill are proposed.