The utility model provides an ethylene cracking furnace. Each radiation furnace tube comprises a first pass tube, a second pass tube and a connecting part that connects the first pass tube and the second pass tube; the two pass tubes are arranged on the same plane, and the connecting part is distributed on both sides of the plane where the furnace tube is located. Thus, the center of gravity of the furnace tube is located in the plane, at the same time, as the first pass tube and the second pass tube are respectively fixed together, when the second pass tube expands downwards, the connecting part and the first pass tube move regularly along the same direction, thereby preventing the furnace tube from being bent and moving to different directions owing to the center of gravity of the furnace tube not being located in the plane in the heat state operation, and better ensuring that the first pass tube and the second pass tube are located in the central plane of the furnace to avoid the unevenness of heat transfer; meanwhile, the varying of the diameter of the furnace tube leads the furnace tube to better meet the requirements of cracking reaction with better cracking performance. The cracking furnace of the utility model has the advantages of long running period, good mechanical property and long service life.