Based on the outstanding optical properties of CdS and excellent electronic properties of single walled carbon nanotube (SWCNT), nano-CdS particle/SWCNT composite materials and nano-CdS/polyethyleneimine (PEI) functionalized SWCNT composite materials are prepared. Their optical and the electrical properties are investigated by using fluorescent light simulated sunlight. The results show that nano-CdS/SWCNT composite material displays a significant negative photo-conductivity phenomenon, while nano-CdS/PEI-SWCNT composite material displays a positive photo-conductivity phenomenon, which can be were explained by using electron-transfer theory. The optical and the electrical properties of two samples are unchanged in the case of large angle bending. Therefore, the nano-CdS/SWCNT composite materials in optical and electrical areas, especially in the emerging field of flexible opto-electronics have a good prospect.