Site-selectively array of single walled carbon nanotubes (SWCNTs) is one of the key points for the fabrication and application of nanodevices. This research is focused on developing a technology to assemble site-selective high density SWCNTs on flexible substrate. Patterned SWCNTs were assembled on flexible poly (ethylene terephthalate) (PET) substrate via inducing directed charge (DC) field. In this process, the modification of hydrophilic or hydrophobic substrate surface is accomplished by selective ultraviolet (UV) irradiation, and which is very important to the self-assemble behavior and accurately site-selective location of SWCNTs. This method, a composition of “Top-Down” approach and “Bottom-Up” approach, is expected to give a way for the fabrication of nanodeivces and nanosystems.