In order to study the exhaust heat recovery potential and influencing rule of a thermoelectric generator （TEG） used in a vehicle， a system model of engine with electronic cooling system and TEG was built with the GT-Suite software， and an overall efficiency criterion for the system considering the whole energy flow was proposed. The effect of the TEG on the overall system efficiency was studied under different engine operation conditions and at different cooling temperatures. The results show that based on an integrated electronic cooling system， the overall system efficiency at low engine speed can be improved by the TEG and it increases as engine load increases. But at medium and high engine speeds the influence of cooling power consumption becomes more prominent. At heavy load， the overall system efficiency will deteriorate because of too much cooling power consumption. Only at low and medium loads can the overall system efficiency be improved by the TEG. There is a best cooling temperature that can make the overall system efficiency maximum.