The vehicle engine exhaust wastes heat. For the conventional scheme, the hot-end of the thermoelectric module is connected with the exhaust pipe, while the cold-end is cooled through the vehicle engine cooling cycle. The variation of vehicle engine operating conditions brings the instability of the hot-end temperature, which affects the power generation performance of thermoelectric materials and increases the damage risk to the thermoelectric materials caused by the high temperature. This research adopts the heat transfer oil circulation as the intermediate fluid to absorb the dynamic heat flux of the vehicle engine exhaust so as to release the heat steadily to the hot-end of the thermoelectric module. The thermal characteristics of the target diesel vehicle engine exhaust gas are evaluated based on the experimental data firstly. Then, the mathematical model of the thermoelectric evaporation system is built on the basis of the geometrical parameters and the specific vehicle engine conditions. Finally, the power generation characteristics of the thermoelectric evaporation system are estimated corresponding to the whole working conditions of the diesel vehicle engine. The results show that the heat transfer oil circulation can lower the temperature gradient of thermoelectric modules hot-end to only 10 percent. Relatively stable power generation could be obtained and the service life could be extended effectively.