Laminar flow diffusion combustion appears when liquid ethanol passes through the ceramic tubes with inner diameter of 1.0 mm, 0.6 mm and 0.4 mm and outer diameter of 2.0 mm. Due to the limitation of measurement tools, it is very difficult to measure the microflame characteristic parameters and the numerical simulation method for microflame is always employed. By comparing the simulation results and measured values, liquid droplet radiation heat transfer and boundary slip have significant effect on numerical simulation and the numerical simulation values agree well with the experimental data, which proves that the numerical simulation method is reliable. The numerical simulation results show that the flame height and width increase almost linearly with the volume flow while the maximal temperature of flame increases first and then decreases. Because the microscale effect can improve the combustion efficiency, A flame with smaller height and width and lower maximal temperature is observed at a lager inner tube diameter.