The utility model provides an anti-theft chamber for the mouth of an oil well. The anti-theft chamber for the mouth of the oil well comprises two side boxes, clamping plates and an upper covering plate, wherein the two side boxes are each in an L shape, the two side boxes are oppositely arranged to form a hollow square, the inner side face of the top of each side box is concave inwards to form an inward-concave boss, the clamping plates are connected between the two side boxes and are located on the inner sides of the side boxes, the upper covering plate is embedded in the inward-concave bosses of the two side boxes and are fixed to the inward-concave bosses through positioning bolts, and a hoisting ring is detachably connected to the top of the upper covering plate. The anti-theft chamber for the mouth of the oil well is of a split structure and is simple in structure, convenient to carry, convenient to install and not easy to open after installation, all ground fittings of a long-closed well can be effectively prevented from being stolen, and safety and environment accidents are eliminated.