Abstract: Disclosed is a cover structure for an airtight container and mainly includes a convex round top plate having a downward projected bottom flange around an outer periphery thereof, a middle annular member defining a central opening and having an upward projected wall around the central opening for fitly abutting on an inner surface of the bottom flange of the top plate, a round box defining an upward open space for positioning desiccative packages therein and having equally spaced vents formed on a bottom thereof, and an elastic silicone seal ring put beneath the middle annular member and around the desiccative box. The upward projected wall of the middle annular member is provided along an inner surface with equally spaced guide ways each of which has a retaining block located at a lower middle point thereof. The desiccative box is provided along its upper outer periphery with radially outward projection corresponding to the guide ways on the middle annular member.