The invention provides an anti-theft lock cylinder which comprises an outer lock cylinder, an inner lock cylinder, a locking tappet and a spring. The invention has the characteristics that: the lock cylinder is provided with a device for closing a keyhole comprising a dynamic spring, a resistance spring, a bearing spring, a lever and a spring, wherein, the dynamic spring is connected with the lever which is connected with the resistance spring; the resistance spring moves and contacts the bearing spring and closes the keyhole, thereby preventing an unlocking tool from inserting; the lock cylinder is also provided with a vertical and horizontal spring device which consists of an upper vertical spring, a lower vertical spring, a back vertical spring, a horizontal spring and a spring, wherein, the upper vertical spring contacts the horizontal spring and leads the horizontal spring to control the inner lock cylinder to rotate; the lower vertical spring contacts the back vertical spring and leads the back vertical spring to control the inner lock cylinder to rotate. The invention is provided with the device for closing the keyhole and the vertical and horizontal device based on the structure of general lock cylinders, and has the characteristics of reasonable structure, prevention of unlocking by inserted unlocking tools, good anti-theft performance, wide application range, etc.