Heat sink does affect on the performance of thermoelectirc generator according to the studies of many authors. In this paper, an analytical model inculding the number of thermocouples and the thermal resistance of heat sink is derived. The match between the thermoelectric module and heat sink is discussed by numerical calculation also. The results show that the thermal resistance of thermoelectric module should be designed to match that of heat sink in order to get the highest output power for a given heat sink. But for a given thermoelectric module, the output power increases with the decrease of heat sink thermal resistance, and there is a suitable heat sink due to the limit of the temperature difference between the heat source and coolant.