The complex transfer and reaction processes happened in ethylene furnaces were taken into consideration. A comprehensive mathematical model was developed with CFD technique based on the following knowledge: (1) basic transport equations of hydrodynamics, (2) k-epsilon-turbulence model, (3) cracking reaction kinetic model developed by Wang, (4) presumed probability-density-function model for turbulent diffusion combustion, and (5) discrete ordinates method for radiative heat transfer. The simulation results showed detailed information about flow and temperature fields, heat flux distribution, and concentration distribution. They provided thorough understanding on the basic characteristics of hydrodynamic phenomena and reaction behaviour occurring in industrial ethylene furnaces. Parametric studies were carried out to investigate quantitatively the influence of burner staging, tube diameter and spacing on operation performance of ethylene furnaces. The comprehensive mathematical model and computational scheme presented here can be used as a tool for the design of ethylene furnaces.