The tailpipe idle noise of a new car model severely exceeds the manufacture’s limits． The reason of inadequate lowfrequency anechoic performance and structural imperfection are obtained by analyzing the transmission loss of the muffler and the muffler’s interior flow field． The front muffler is optimized by using the crossflow perforation structure and the main muffler’s perforation form is improved． GT-Power simulation and test results show that lowfrequency anechoic performance of the muffler is improved，and the tailpipe idle noise decreases by more than 4dB( A) and 3dB( A) respectively at AC off and AC on cases． The total tailpipe sound pressure levels and the back pressure of the exhaust system at the 3WOT case satisfy the manufacture’s technical requirements．