Abstract: Numerical simulations were conducted on the heat transfer and working fluid flow in the membrane wall of a supercritical pressure Zhundong coal-fired boiler according to the fluid-solid coupling heat transfer theory, while a mathematic relationship between contamination factor and slagging thickness was fitted. Results show that when the slagging thickness increases from 10 mm to 30 mm, the contamination factor would drop by 50%, and when the slagging thickness lies in 30-50 mm, the contamination factor would change slightly. With the rise of average flame temperature, the contamination factor reduces significantly. The fitting function obtained can be used in design, calculation and slagging control of power plant boilers.