Abstract: Traditional optical imaging technology can only detect targets within the range where light can reach, and is usually ineffective for targets outside the field of view. Non-line-of-sight (NLOS) detection makes use of single-photon extreme sensitivity detection and time-correlated detection with fine temporal resolution. By means of computational imaging, it reconstructs the scenes beyond the field of view, making the detection of concealed targets possible. This review introduces the background of NLOS detection technology, points out the current technical difficulties and challenges, systematically expounds the characteristics and current situations of the main technical approaches, analyzes and compares the technical advantages and key problems of each main technical approach. The research results are expected to provide feasible technical routes to break through the technical bottlenecks of NLOS imaging in terms of detection capability and operating range. Moreover, they will further promote the innovative development of NLOS detection mechanisms, methods, technical systems and devices, and ultimately provide strong impetus for the development and application of NLOS detection technology in both military and civilian fields.