The purpose of this study is to investigate NOx reduction. This study were conducted by changing kinds of urea, and suppling combustion air at municipal waste incinerator appling the SNCR system in Go-yang. We obtained 15% NOx reduction when change kinds of urea, but ignition loss and CO concentration increased 5.49%, 24.9% respectively. The NOx concentration decreased with increasing NSR(normalized stoichiometric ratio) from 132ppm to 32ppm. NOx reduction is increased with increasing combustion air(primary air, secondary air)