Abstract: The present disclosure provides an oral cone beam X-ray imaging system and its fast positioning method. The working modes of the imaging system includes an oral CT shooting mode, an oral panoramic shooting mode, and a head frontal and lateral shooting mode. The system includes a source, a flat panel detector, a rotating driving device, a data processing device, and a control device. The number of sources, flat panel detectors, and rotating driving devices is one to form a single-path imaging system. The working mode also includes a fast positioning mode to perform Self-Adaptation positioning of the imaging system based on the positioning result of the fast positioning mode. In the rapid positioning method, low-dose X-rays are emitted; CT images are received and reconstructed to obtain the current pose of the measured object; and based on the current pose, the imaging system performs Self-Adaptation positioning to perform imaging in the oral panoramic shooting mode or the head lateral shooting mode.