When the truck is unloaded into the loading and unloading area, its rear end touches the integral steel frame of the built-in spring, pressing the steel frame downward and allowing the rear to fully reverse and reach the steel frame. Then the operator presses the control button to lift the pull hook, hooking the rear crossbar. This hook can withstand pulling forces up to 16 tons. During loading and unloading, the locking device automatically adjusts the height of the rear float and the fixation of the rear crossbar to ensure safety. When loading and unloading are completed, operators press the control button to lower the hook. When the truck deviates or the rear crossbar is no longer effectively locked, the locking device will enter an incorrect working state, at which point the warning device will issue an alert to the operator that the truck is not properly locked.