The　thermal　decomposition　of　aqueous　urea　solution　was　studied　in　a　lab-scale　experimental　system,　and　the　experimental　research　was　focused　on　the　effect　of　O2　concentration　on　the　NH3　yield.　It　was　found　that　O2　could　promote　the　thermal　decomposition　and　enhance　the　NH3　yield　in　the　temperature　range　of　473-773　K,　while　the　NH3　yield　dropped　rapidly　as　the　reaction　temperature　increased　from　823　K　to　1073　K　in　the　presence　of　O2.　Without　O2,　the　NH3　yield　increased　gradually　as　temperature　increased　from　473　K　to　923　K　and　remained　60%　approximately　in　the　temperature　range　of　923-1073　K.　In　the　presence　of　5%　O2,　the　highest　NH3　yield　reached　59.1%　at　823　K,　while　it　reached　59.8%　at　773　K　in　the　presence　of　10%　O2.　The　Urea2000　model　was　adopted　to　simulate　the　reaction　process,　and　the　modeling　results　were　plotted　in　comparison　with　the　experimental　data.　The　experimental　data　and　the　modeling　results　agree　qualitatively,　but　they　differ　quantitatively　when　the　temperature　ranged　from　873　to　1023　K　in　the　presence　of　O2.　Therefore,　several　changes　were　made　on　elementary　reactions　related　to　O2　in　the　Urea2000　model　to　make　it　accurately　describe　the　thermal　decomposition　process　and　properly　predict　the　NH3　yield.