The present disclosure provides a mask plate, a mask exposure device and a mask exposure method, belongs to the field of display technology. The mask plate includes a tray with at least one mask locating slot, and a mask is arranged in each mask locating slot. By the mask plate, the mask exposure device and the mask exposure method provided by the present disclosure, an effective mask with a closed-loop shaped opening may be provided, thereby improving a quality of a film formed on a substrate.