Abstract: Thermoelectric devices can realize the direct conversion between thermal energy and electrical energy, showing great potential for waste heat recovery and cooling. To evaluate the performance of thermoelectric materials and devices, it is of great significance to accurately measure the heat-to-electricity energy conversion efficiency of thermoelectric power generation devices. Aiming at the problems of many measurement parameters and wide error sources in the measurement process, this article starts from the measurement principle, detailed analysis of factors affecting energy conversion efficiency measurement by formula derivation and reasonable assignment, and it is highlighted that the measurement accuracies of both output power and cold-side heat flow are critical for the evaluation of the conversion efficiency of thermoelectric devices. Specifically, the output power would be decreased with the increase of interfacial electrical contact resistance. In addition, accurate measurement of cold-side heat flow can be obtained when a suitable reference sample with an optimal dimension and thermal conductivity is used. Moreover, consideration of radiation heat is also needed when the hot-side temperature is high. Finally, recent progress and challenges of thermoelectric power generation devices are discussed.