The test of combustion of chemical sludge and municipal sewage sludge were conducted in a tubular furnace focusing on the influences of moisture content,combustion temperature and sludge type on the emission of NO_x.The way to get the sludge with specified moisture content was illustrated in detail and specific steps were listed.The results indicate that with the increase of moisture content from 5% to 35%,the emission of NO_x decreases significantly during the combustion of chemical sludge and municipal sewage sludge.Increasing the combustion temperature from 700 ℃ to 900 ℃ can also increase the emission of NO_x.The emission of NO_x during the combustion of chemical sludge is higher because the metal oxides contents in the chemical sludge are higher than those in the municipal sewage sludge.Depending on the generating mechanism of NO_x,a detailed analysis of these conclusions was made,and these results will provide a positive guidance to the control of NO_x emission in the boiler.