Photodetectors play a key role in various demanding applications, such as remote sensing, night vision, reconnaissance, medical imaging, thermal imaging and chemical detection, etc. Structures and features of the photodetecting materials directly affect the performance of the photodetectors. In recent years, carbon nanotubes (CNT) have rapidly grown into the alternative materials in photodetection due to their unique optical and electrical properties. The early researches were mainly focused on photodetectors based on individual carbon nanotubes, while potential applications require carbon nanotube thin films as the detecting layers to maximize the photo absorption ability and the detective efficiency. Therefore, preparation of large-area, high-density, high-orientation, and high-uniformity carbon nanotube thin films, and fabrication of the photodetectors based on these thin films, have attracted great research interest in the field of CNTs. Herein we elaborate the development of preparation methods of CNT thin films as well as the recent progress in the CNT-based photodetectors with a discussion on its development tendency in the near future..