Thermoelectric generators (TEGs) are usually working in intermittent heat source environments, and thus the phase change material (PCM) has been widely adopted in to maintain relatively stable temperature difference. The temperature of cold-end of TEG is one of the crucial factors to influence the performance of the PCM-TEG system. In this work, the influence of the cold-end temperature of the TEG on the generated electricity of PCM-TEG system is studied. Classic Enthalpy model and three-dimensional coupled thermo-electric equations are applied to study the heat transfer and energy conversion mechanisms. Our results show that the output electric energy of a PCM-TEG system can be optimized by tuning the phase change temperature of PCM. The total generated electricity can be enhanced as large as 15.6% by matching the PCM with the thermoelectric properties of the thermoelement. Moreover, by comparing three cases with different thermoelectric materials, we give relationship between the optimal phase change temperature of PCM and the temperature for maximum figure of merit (ZT) of the thermoelement, which provides a selection criterion of PCM for TEG module. Our work could be helpful to realize further high efficiency thermoelectric generators for intermittent heat sources.