Terahertz quantum well photodetectors (THz QWPs) are ultra-fast devices, which have picosecond response time and more than 1 GHz modulation speed. THz QWPs have great potential applications in the field of THz fast imaging and high-speed wireless communications. This paper summarizes the principle, design, performance and recent research progress of THz QWPs. Research shows that the fast imaging system based on THz QWPs can detect the detailed information of the object, which is expected to be used in the field of safety inspection and nondestructive testing. Additionally, THz QWPs can be used as the detection end of high-speed wireless communication, providing an effective technical approach for future 6G wireless communications.