The invention relates to an anti-arrearage low-voltage three-phase four-line ammeter casing which is so structured that an ammeter is connected to a load-side connecting row, a grounding protection connecting row and an air switch, the air switch is connected with an opening tripping switch, an opening tripping coil and an arrearage tripping coil are arranged on the air switch, two contacts of the power switch are respectively connected with the opening tripping coil and the arrearage tripping coil, and a current transformer is connected with a three-phase lead and arranged above the ammeter. The occurrence of electric power client arrearage on purpose can be prevented. The lock structure is simple and practical, and loss of protection function of an ammeter casing due to damage of connecting rod lock can be prevented. The appearance is simple and beautiful, and the production cost and maintenance cost of a power supply enterprises can be reduced.