The invention belongs to a rolling method of steel plates, and particularly relates to a rolling method of the grain size of stainless steel plates used for controlling thermonuclear fusion reactors. The rolling method includes the steps of steel ingot heating, blooming, raw material plate heating, hot rolling and steel plate cooling. In the step of steel ingot heating, firstly, steel ingots are heated, the starting temperature of heating is 700 DEG C, the temperature is kept for 1-2 hours, and then the temperature is slowly raised to 900 DEG C; the 900 DEG C temperature is kept for 6-6.5 hours, then the temperature is continuously raised to be between 1200 DEG C and 1310 DEG C, and lastly, the temperature is kept between 1200 DEG C and 1310 DEG C for 3-4 hours. In the step of raw material plate heating, firstly, the starting temperature of heating is 700 DEG C, the temperature is kept for 1-1.5 hours, and then the temperature is raised to 900 DEG C; the 900 DEG C temperature is kept for 5-5.5 hours, then, the temperature is continuously raised to be between 1200 DEG C and 1310 DEG C, and lastly, the temperature is kept between 1200 DEG C and 1310 DEG C for a period of time. The rolling method has the advantages of enabling the grain size of the steel plates to be between grade 6 and grade 8 steadily though controlling the time duration of heat preservation in different stages and controlling the rolling process.