The temperature of exhaust gas was raised by increasing of engine movement on developing engine. Thermal of high temperature and pressure reverse in bellows, because of increasing of engine movement and the thermal performance of converter in combustion. As a result, thermal loss is increased and thermal efficiency is decreased rapidly in bellows, it can occur to damage in mechanical structure. In this study, it was necessary to analyze back pressure performance and thermal characteristic on driving condition in exhaust system. It was adapted braid type bellows and straight type exhaust pipe. It was compared with curve type exhaust pipe for lay-out on considering to design of exhaust system. It was necessary to improve thermal characteristic and back pressure performance so that expansion cavity pipe(ECP) was installed between bellows and catalyst convert. Not only decreasing back pressure was solved but also thermal characteristic problems in exhaust pipe because of increasing capacity. According to this study, the basis of data is presented when new exhaust system is designed.