The present invention relates to a metal photomask box structure, which is composed of an upper cover member, a lower cover member, and a ring-shaped airtight washer positioned between the upper metal cover member and the lower metal cover member. At least a movable connecting mechanism is disposed on one side of the metal photomask box to connect the upper metal cover member and the lower metal cover member. And at least a latch piece is disposed on an opposite side of the movable connecting mechanism to latch the upper metal cover member and the lower metal cover member.