The soot blowing performance for a wall blower, according to the entering distance of a nozzle from the boiler wall, is evaluated according to a liquid droplet impingement erosion model. This erosion model incorporated the computational fluid dynamics of a jet steam of nozzle, and it uses the pressure and velocity of a jet steam at the furnace wall for several entering distances of the nozzle. A relative erosion rate dependent on the velocity of the jet steam is also introduced. Several cases are compared, as determined according to the entering distance and the number of nozzles. The shaded erosion region, according to the entering distance of the nozzle and the co-injected region, have also been schematized. Specifically, when the entering distance of the nozzle is large, the maximum relative erosion rate is small. However, the soot blowing area is uniformly large, as compared with the case of a small entering distance. This shows that the maximum relative erosion rate is high, but the soot blowing region is small and the shaded regions occur.