The production of ethylene by cracking furnace is the most commonly used method in industrial and furnace tube is the main place where cracking reactions occur. The internal components of the twisted slices are added to furnace tube and the purpose is to improve the coupling between the flow field and the temperature gradient field, so as to enhance the heat exchange of the fluid and to promote the increase of products in the cracking reaction. U-shaped tube of ultra-selective cracking furnace was selected as the research object, based on naphtha cracking raw material. The furnace tubes were built into different multiple groups of twisted slices for numerical simulation to obtain the temperature distribution and the mass fraction distribution of ethylene and other products. Simulation results showed that the twisted slices can effectively reduce the temperature gradient between the tube wall and the core fluid, and the heat exchange effect of the furnace tube with 3 groups of twisted slices placed in the outlet section was the best. The yield of ethylene and butadiene in the furnace tube increased linearly along the axial distance, while the yield of propylene decreased at the exit stage in the later period of reaction. The L2R3-type tube with two twisted slices placed in the inlet section and three twisted slices placed in the outlet section had higher yield of triene, which was 1.29 times that of the smooth tube.