The physical field, furnace tube heat intensity and NO production of different heating furnaces were studied through numerical simulation. Firstly, by studying the heating furnaces of different shapes, namely triangle furnace, square furnace and cylindrical furnace, it was found that the heat intensity of the cylindrical furnace tubes was evenly distributed, but the NOX emission at the outlet of the cylindrical one was relatively higher than that of the square one. By studying the cylindrical furnaces with different dip angles of 95°, 93°, 90°, 87° and 85°, it was found that the NOX emission at the outlet has been effectively reduced with the decrease of the dip angle, but the heat intensity of furnace tubes was more unevenly distributed, which led to more serious tube coking.