Thermoelectric (TE) devices can realize the conversion of heat energy and electrical power based on Seebeck effect and Peltier effect. Among them, flexible TE devices have received more attention recently due to their better attachment to various heat sources and aimed components with arbitrary shapes. To improve the performance of flexible TE devices for various application scenarios, large efforts have been made to design the leg patterns, the electrical and thermal contact issues, and the substrate and encapsulation materials for the decrease of heat loss. This paper is to review the advancements about the design of flexible inorganic TE devices over the last decade. Firstly, the design of flexible thin-film TE devices based on the direction of temperature gradient, including the patterns of TE legs, the fabrication methods, and the flexible substrate materials is summarized. Secondly, the design of wearable TE devices that contains common architecture of the module, the substrates and encapsulations, the electrical and thermal contact, and some thin-film based wearable devices with curving TE legs is demonstrated. Thirdly, the characterizations of the flexibility of TE devices and the current applications are outlined. Moreover, some views about the future development for TE devices are proposed.