The invention discloses a trip pulley capable of automatic locking, belonging to the field of power supply system. The trip pulley comprises a hook and a pulley body, the hook is composed of a pedestal and an inverted U-shaped link on the pedestal, an opening is formed at one side between the link and the pedestal, a pulley wheel I is vertically hinged to the two sides of the link and arranged in the link, the upper end of the link is hinged to a connecting plate which is driven by the self gravity, the end portion of the connecting plate is hinged to an arched locking pin, an arched opening of the locking pin is opposite to the hook, and the other end of the locking pin is sealed by the opening between the link and the pedestal. According to the trip pulley capable of automatic locking, the opening through which leads are output/input in the pulley can be automatically closed and opened, safe work of operation staff is ensured, the operation staff is avoided from the complexity of manual control, and operation is more convenient and rapid.