The　selective　catalytic　reduction　(SCR)　technology　is　considered　as　a　highly　efficient　and　promising　after-treatment　technology　for　deducing　the　diesel　engine　NOx　emission.　The　temperature　inside　an　SCR　catalyst　container　is　important　for　NOx　conversion　efficiency　and　SCR　control　precision.　Accurate　prediction　for　the　temperature　of　the　SCR　catalyst　under　the　condition　of　transient　loads　has　important　influence　on　the　NOx　conversion　efficiency.　In　order　to　gain　the　detail　of　the　temperature　distribution　inside　the　SCR　catalyst　container,　this　work　designs　5　test　plates　with　thermocouples　which　are　mounted　inside　the　SCR　catalyst　container　in　different　places.　These　5　test　plates　contain　a　serial　of　thermocouples　located　in　different　position　to　test　the　temperature　distribution　inside　the　SCR　catalyst　container.　These　5　plates　are　orderly　located　from　the　inlet　to　the　outlet　of　the　container,　and　in　each　plate,　there　are　totally　17　test　points　successively　along　2　diameters　which　are　respectively　the　horizontal　and　vertical　directions.　During　the　experiment,　the　diesel　engine　with　the　SCR　system　is　tested　under　the　varied　operation　engine　speeds　and　loads　to　supply　the　SCR　catalyst　container　with　exhaust　gases　of　different　temperatures　and　mass　flow　rates.　In　addition,　a　mathematic　model　is　proposed　to　predict　the　catalyst　temperature　at　the　outlet　based　on　the　tested　inlet　temperature　data　of　the　SCR　catalyst　container.　The　mathematic　model　is　solved　based　on　a　program　which　is　compiled　by　Matlab/Simulink　codes.　The　experimental　results　show　that　under　the　steady　conditions,　the　temperature　inside　the　SCR　catalyst　container　decreases　from　the　inlet　to　the　outlet　of　the　container　along　the　axial　direction.　The　reason　is　that　as　the　exhaust　gas　flows　through　the　SCR　catalyst　container,　the　thermal　energy　of　the　exhaust　gas　decreases　due　to　the　thermal　energy　exchanges　such　as　heat　convection,　heat　conduction　between　the　exhaust　gas　and　the　catalyst　carrier,　the　container　wall,　as　well　as　the　environmental　atmosphere.　The　experimental　results　also　show　that　the　outlet　temperature　is　lower　than　the　inlet　temperature,　and　the　maximum　deviation　between　the　tested　inlet　temperature　and　outlet　temperature　is　10.1%.　However,　the　model-predicting　outlet　temperature　has　a　better　deviation　of　6.2%　with　the　tested　outlet　temperature.　Under　the　conditions　of　transient　operation,　the　downstream　temperature　of　the　catalyst　container　shows　a　delay　of　temperature　increasing.　As　the　engine　speeds　and　loads　change,　firstly　the　inlet　temperature　rises,　but　the　downstream　temperature　doesn＇t　increase　together　with　the　inlet　temperature,　and　it　begins　to　rise　after　40　s.　The　downstream　temperature　reaches　its　95%　of　the　maximum　after　nearly　380　s.　The　reason　of　this　temperature-increasing　delay　is　that　the　thermal　energy　transfer　from　the　exhaust　gas　to　the　SCR　catalyst　especially　under　the　transient　condition　takes　much　time,　and　the　narrow　catalyst　holes　cause　flow　resistances　to　the　exhaust　gas.　This　temperature-increasing　delay　is　also　demonstrated　by　the　mathematic　model.　In　addition,　the　model　predicts　that　the　outlet　temperature　under　the　transient　condition　has　a　deviation　of　less　than　6%　which　is　better　than　the　deviation　between　the　tested　inlet　temperature　and　the　outlet　temperature　(32%).　Therefore,　the　inlet　temperature　of　the　SCR　catalyst　container　is　not　suitable　to　be　simply　adopted　as　the　outlet　one　for　the　purpose　of　the　SCR　system　control　strategy,　because　there　is　great　deviation　between　the　inlet　temperature　and　outlet　temperature　under　both　steady　and　transient　operation　conditions.　In　this　work,　the　proposed　mathematic　model　shows　good　calculation　precision　when　predicting　the　outlet　temperature　under　both　steady　and　transient　operation　conditions.　Compared　with　the　simple　method　of　adopting　the　inlet　temperature　as　the　outlet　one,　this　model　for　predicting　outlet　temperature　has　better　control　precision　especially　under　transient　conditions,　which　is　good　for　SCR　system　control　strategy.　The　control　algorithm　is　applied　to　the　SCR　system　of　a　heavy-duty　diesel　vehicle,　and　the　vehicle　is　tested　based　on　the　ESC　(European　steady-state　cycle)　and　ETC　(European　transient　cycle)　test　standards.　The　tests　show　that　NOx　emission　is　lower　than　the　limit　of　the　China　IV　emission　standard,　which　demonstrates　the　proposed　algorithm　meets　the　control　requirements　of　the　vehicle.　©　2016,　Chinese　Society　of　Agricultural　Engineering.　All　right　reserved.