Herein, we demonstrate a concept of making flexible thermoelectric (TE) generators by applying cotton thread as the platforms for poly(3-hexylthiophene) (P3HT) and Argentum (Ag) paste through selectable coating method. The coated thermoelectric cotton thread can be sewed on the flexible fabrics with different knitting pictures and form thermoelectric devices. The most important is that the temperature gradient of the device was in the direction of cross-plane of the flexible fabrics, that is, between the inner and outer surfaces of clothing, therefore the flexible device can be easily wore on the body since the temperature gradient between the human body and surrounding environment is in the cross- plane direction. The maximum output power of the device with thirteen P-N type legs reached 1.15 mu W at a temperature gradient of 50 K when the load resistance matched the resistance of the module. Cotton-based TE device coated with P3HT may be useful for the development of self-powered wearable electronics.