Abstract: Analyzed in the article are the critical technological requirements for hot rolling of square and rectangular tubes. According to the equipment configuration of a certain plug pipe mill plant，product development is carried out，involving pass design，design of property control and control of product appearance，and eventually hot-rolled square and rectangular tubes with sizes as 140 mm×140 mm，150 mm×160 mm and 200 mm×200 mm are successfully trial produced. The result of the trial production shows that both the geometric dimensions and the mechanical properties of the hot-rolled square and rectangular tubes can be assured provided relevant proper controls are guaranteed，including consistency of wall thickness and OD of the round blank pipe，deformation amount distributions of the round pass and square pass of the sizing mill，design of the roll surface curvature of pass of the square and rectangular tubes，rolling temperature，steel type selection，and contents of C and Mn，and optimization of cooling speed，etc.