The　low-temperature　catalytic　pyrolysis　of　sludge　is　a　new　developing　technology　with　the　dual　characteristics　of　sludge　treatment　and　energy　recovery.　It　was　used　to　treat　residual　sludge　produced　by　an　urban　wastewater　treatment　plant.　Pyrolysis　conditions,　like　residence　time　and　final　pyrolysis　temperature　and　catalyst,　were　varied　so　that　their　influence　on　the　characteristics　of　the　resulting　products　could　be　studied.　With　the　help　of　thermal　gravimetric　analysis　(TGA)　for　residual　sludge　and　GC/MS　analysis　for　derived　oil,　it　was　discussed　about　the　reaction　mechanism　of　pyrolysis　process.　Results　showed　that　using　catalyst　decreased　the　char　fraction　yield　and　increased　the　oil　fraction　yield　while　that　of　the　quality　of　oil　also　improved.　Furthermore,　the　final　pyrolysis　temperature　needed　for　maximising　the　fuel　oil　yield　fell　from　450　C　to　400　C,　maximum　oil　yields　increased　from　34.53%　to　38.71%,　and　the　heating　value　of　oil　was　higher.　The　main　reaction　mechanism　could　be　presumed　the　evaporation　of　aliphatic　compound　and　the　conversion　of　protein　from　200　C　to　450　C.　©　2011　IEEE.