Abstract: The effects of structural dimensions such as central tube equivalent radius, branch tube equivalent radius, tube spacing, and tube length on the performance of a flat double-P type radiant tube were studied in this paper. The structural dimensions of the radiant tube and the positions of the burner nozzles were optimized using an orthogonal experimental program. It is shown that obvious influencing factors on the surface temperature difference of the radiant tube are tube spacing, central tube equivalent radius, tube length, and branch tube equivalent radius in turn. However, significant influencing factors on the radiant power of the radiant tube are tube length, central tube equivalent radius, tube spacing, and branch tube equivalent radius in order. When the size ratio of the upper to lower air nozzle is 7:3 and the size ratio of the left to right air nozzle is 9:1, the performance parameters of the radiation tube are the best. When the distance between the air and fuel gas nozzle is 50 mm and the air nozzle distance is 60 mm, the uneven coefficient of the radiation tube's surface temperature is the smallest at 0.058.