The QKD system based on the BB84 protocol is a dedicated teaching system developed based on the training demands of quantum mechanics, physics, optical communications and other related majors. This system adopts modular design and involves a series of experiments, including single photon characteristic test, state preparation, encoding, transmission, detection in QKD system, realization of post-processing algorithm of QKD protocol and key storage and management, and provides the key output interface. The system type supports fiber channel and free-space channel.