Near-infrared (NIR) polymer photodetectors possess flexible and adjustable photoelectric characteristics, have good compatibility with flexible substrates, require a simple preparation process, and are inexpensive. They also have significant application prospects in aviation, military, industrial, and medical fields. NIR polymer photodetector structures include photoconductors, photodiodes, and phototransistors. This study reviews the research progress of NIR polymer photodiodes (NIR PPDs). First, the photoelectric conversion principle of NIR PPDs is introduced. Second, important advances made by researchers in improving the performance of NIR PPDs from the perspectives of new material development and device structure design are discussed. Finally, a summary is presented along with possible challenges and prospects of current research on NIR PPDs.