Abstract: To study influence of oxygen on distribution and transformation of fuel-N, pyrolysis experiments of straw were conducted in a two stage fixed bed reactor simulating the run conditions of grate firing. The conversion pathway of fuel-N was depicted by studying types and content of N-containing compounds in tar by GC-MS, and effect of oxygen was analyzed. Compared with inert atmosphere, tar and char yields decrease with introduction of oxygen, which leads to a decrease of N-distribution in tar and char and increase in gas fractions. Protein and amino acids are the main N-containing components in fuel, which initially go through a series of primary reactions, producing primary tar components like amides and amines. Then the primary tar goes through secondary reactions to yield secondary tar components including nitriles and N-heterocyclic compounds. In the presence of oxygen, content of primary tar components like amides and amines decrease significantly, and secondary tar components like nitriles and N-heterocyclic compounds increase.