The invention relates to the field of light boxes, in particular to a display module in a modular light box. The display module comprises a panel module, a substrate module, an advertisement module and a light source module, wherein the panel module and the substrate module are each divided into multiple rotary plates which can be turned over through rotation, the light source module and the advertisement module are arranged on the surfaces of the two sides of the rotary plates respectively, the panel module corresponds to the rotary plates on the substrate module, and positions of corresponding rotary plates can be interchanged in the light box through a transmission device. The display module in the modular light box allows the service life of a light source to be prolonged, allows advertisements to be freely switched, and allows advertisement cost to be reduced.