Abstract: The present disclosure provides a tensioning mechanism of a box and a light emitting diode (LED) box assembly with the tensioning mechanism of the box. The tensioning mechanism of the box includes a tensioning structure including a base and a tensioning rod, where the base is provided with a mounting portion, the tensioning rod includes a tensioning pin and an operating portion connected with the tensioning pin, and the tensioning pin is movably arranged in the mounting portion in a penetrating manner; and a connecting member provided with a cooperating hole, where the tensioning pin includes a flat shaft, the flat shaft is capable of being inserted into or moved out of the cooperating hole, and under the condition that the flat shaft is inserted into the cooperating hole, the flat shaft has a vertical tensioning position and a transverse unlocking position.