Locating a radiant source based on time difference of arrival (TDOA) measurements using spatially separated receivers has wide applications. Although extensive research works have been performed on development of TDOA localization solution, limited attention has been paid to sensor array geometry design. However, the sensor array geometry has a significant influence on the localization accuracy. Therefore, in this paper, the comparison between the localization performances of different sensor array geometries is investigated by numerical simulation. Several factors of sensor array geometry are taken into account in the model, which have an obvious effect on the localization accuracy. Finally, an optimum three-dimensional sensor placement is obtained with four sensors. The research results are very valuable for practical engineering applications.