The invention discloses a flat double P type radiant tube which comprises a first straight tube, a three-way tube, a second straight tube, a third straight tube, a first bent tube and a second bent tube. A burner is fixed into a first straight tube mounting pipe, a central spray tube is a gas jet, four spray tubes on the outer side are air jets, the sections of all the spray tubes are elliptic, the proportion of a long edge and a short long edge of an ellipse is as same as that of a long edge and a short long edge of the section of a radiant tube body, and the first straight tube and the three-way tube are thickened. The flat double P type radiant tube has the advantages that the thickened first straight tube can effectively prevent tube wall failure caused by high-temperature corrosion, the thickened three-way tube can prevent bent tube deformation caused by heat stress, and the section of the radiant tube body is elliptic. Compared with a circular radiant tube consuming the same alloy steel, the effective radiant area of the radiant tube for a workpiece is enlarged, and the heat exchange amount of the radiant tube and the workpiece within unit time is increased. Burning flame diffuses towards two sides of the radiant tube, the radiant temperature of two side wall surfaces of the radiant tube is increased, and the temperature of the radiant tube is uniformly distributed.