Abstract: Velocity of the flue gas of boiler convection heating surface is an important factor to the economy and safety of boiler design and operation it affects the quantity of metal consumption of boiler manufacture and the working reliability of boiler service. In the present time the gas velocities used in boiler design in China are mainly referred to the Russian standard, but the characteristics of coals and some other factors of the two countries are not the same, therefore it is necessary to do the research work about this problem. The authors have made a complete analysis regarding to the characteristics of abrasion of coals and have done a series of experiments of different kinds of coals. In the end of this paper, the authors proposed the data of gas velocities which could be used in boiler design and operation in China as reference.