The present invention provides a scan gantry for a medical imaging system. The scan gantry comprises a bottom supporting frame and a tilt supporting frame that are connected to each other, wherein the tilt supporting frame is tiltable relative to the bottom supporting frame. The scan gantry further comprises a locking mechanism connected between the bottom supporting frame and the tilt supporting frame. In the process that the tilt supporting frame is being tilted relative to the bottom supporting frame, the locking mechanism is in an unlocked state; and when the tilt supporting frame is stationary relative to the bottom supporting frame, the locking mechanism is in a locked state to prevent the tilt supporting frame from moving relative to the bottom supporting frame.