The　prediction　and　control　of　ammonia　slip　are　the　key　issues　of　selective　catalytic　reduction　(SCR)　system.　A　SCR　sample　test　bench　was　built.　The　adsorption　and　desorption　characteristics　of　ammonia　in　V2O5-WO3/TiO2　catalyst　are　studied,　and　the　effects　of　NH3/NOx　ratio　and　catalyst　temperature　on　ammonia　slip　are　analyzed.　The　results　show　that　the　ammonia　slip　increases　rapidly　once　ammonia　leaks.　The　prediction　of　critical　point　of　ammonia　slip　is　very　crucial　for　the　control　of　ammonia　slip.　When　the　ammonia　slip　reachs　to　a　critical　point,　the　ammonia　storage　saturation　level　is　not　changed　with　the　change　in　NH3/NOx　ratio　and　catalyst　temperature.　When　NH3/NOx　ratio　is　set　to　0.7,　1.0　and　1.4,　the　ammonia　storage　saturation　level　is　79%,　75%　and　76%.　The　value　of　ammonia　storage　saturation　level　maintains　fluctuations　in　the　rangg　of　about　76.7%　when　the　ammonia　slip　reachs　to　the　critical　point.　The　ammonia　storage　saturation　level　is　related　to　the　ammonia　slip　critical　point.　The　control　method　of　ammonia　slip　is　designed　based　on　the　correlation　between　ammonia　saturation　level　and　ammonia　slip　critical　point.　The　control　method　was　used　for　SCR,　and　the　European　transient　cycle　(ETC)　test　of　engine　was　performed.　The　ETC　test　results　show　that　the　brake　specific　emission　of　outlet　NOx　is　reduced　to　2.45　g/(kW·h),　the　average　ammonia　slip　is　3.7×10-6,　and　the　peak　ammonia　slip　is　12.8×10-6,　which　meet　the　requirements　of　national　IV　emission　regulations.　©　2017,　Editorial　Board　of　Acta　Armamentarii.　All　right　reserved.