The performance of a multi-couple thermoelectric device as a generator is inverstigated. The general expressions of two important performance parameters, the efficeiency and power output, are given. The η-K characteristic curves of a thermoelectric generator are presented for some differently constrained conditions, where η is the efficiency of the thermoelectric system and K is total thermal conductance of the multi-couple thermoelectric device. The mazimum efficeiency of the system if calculated. The structure parameters of the device are optimized. The effect of the thermal conductances between the thermoelectric device and the external heat reservoirs on the performance of the system is expounded by using some representative numerical examples. The results obtained here will be useful for a more detiled investigation and for the optimal design of real thermoelectric generators.