Automotive exhaust-based thermoelectric generator (TEG), which effectively converts exhaust thermal energy into electrical energy, can gradually improve the utilization efficiency of energy. The heat exchanger of TEG is one of the most important components for heat transfer, so as to realize energy saving and emission reduction. Hence, its configuration and thermal performance should be intensively studied.In this paper, a new configuration of heat exchanger, whose heat transfer area is regular octagon, is designed in comparison with the pervious rectangle one. In order to improve average temperature and thermal distribution uniformity, typical CFD software named FLUENT is used to simulate the multi-coupling of temperature - fluid - solid, and the temperature distribution on heat transfer area is gained. Moreover, the temperature distribution will be analyzed to evaluate the merits and weaknesses of configuration and thermal performance. By adopting different guiding fins, setting various height and thickness parameters of guiding fins, varieties of heat exchangers are modeled and simulated. From these simulation results, a relatively supervisor structure and thermal performance of heat exchanger is obtained. Then experimental system based on bench test is carried out. Via infrared images and real bench test data, it is able to verify the reliability and accuracy of simulation results.Eventually, through simulation results and bench test, the heat exchanger is intended to be improved. It is expected to obtain a relatively supervisor structure and highly attractive thermal performance of heat exchanger.