Limited by the methods of information acquisition and signal processing, traditional optical imaging technology can only image targets within the visual range. With the development of new imaging equipment and high-performance computing, nonline-of-sight (NLOS) imaging technology, which integrates optical imaging, computing technology and image processing, makes it possible to image beyond the field of view. Based on the differences in imaging mechanisms, we divide the existing NLOS methods into three categories: methods based on spatial coherence, two-dimensional intensity information and time-of-flight. We analyse the principles and implementations of different NLOS technologies. We focus on the time-of-flight methods and compare their imaging performance under the open dataset, which includes multiple types of targets and indoor and outdoor scenarios. Furthermore, we build a nonconfocal transient imaging system based on a detector array, capture the single-shot nonconfocal transient images and analyse the results of nonconfocal NLOS methods using these captured images. Finally, we prospect the future direction and application of nonline-of-sight imaging.