The invention provides a formation method of I-shaped steel for nuclear fusion reactor magnet supporting. According to the formation method, a main roller die and a core roller die are adopted; the formation method comprises the steps of (1), preparing an annular blank, wherein steel ingots are heated to 1150 DEG C to be forged and pressed, so that the texture state of the steel ingots is changed, internal defects are seamed, and the annular blank is manufactured after a punching procedure and a chambering procedure; (2) conducting ring rolling manufacturing on the I-shaped section, wherein the main roller die is arranged on a main roller of a ring rolling machine, the core roller die is arranged on a core roller of the ring rolling machine, the annular blank is heated to 1150 DEG C, thetemperature is kept for enough time, the annular blank is placed on a workbench of the ring rolling machine, the main roller of the ring rolling machine rotates and feeds until the core roller die and the main roller die feed in place, and formation ring rolling of the I-shaped section is completed; (3) conducting dividing and straightening, wherein the annular piece is divided into multiple arcsections according to arc length, the arc sections are straightened correspondingly, and then the I-shaped steel for nuclear fusion reactor magnet supporting is formed. By the adoption of the formation method of the I-shaped steel for nuclear fusion reactor magnet supporting, the formation speed is rapid, the dimension precision is high, the machining allowance is small, the manufacturing difficulty is greatly lowered, the mechanical performance is improved, the service life is prolonged, and the formed I-shaped steel has low temperature resistance, high pressure resistance and corrosion resistance and is low in machining cost.