Composition and formation cause of the deposits in diesel engine urea-SCR system were investigated with the help of Fourier transform infrared(FTIR)spectrometer and thermal gravimetric(TG)analyzer.Deposits samples were respectively taken from places near the urea nozzle and on the exhaust pipe wall.Results indicate that the two samples of deposits decompose into gas when heated to above 430℃;There are two weight loss stages on the former TG curve in range of 150℃to 250℃the sample decomposes into isocyanic a...