A container cover for storage container includes a rotary device, an outer cover member, an inner cover member, a first guide block, second guide block, a pumping piston and a piston seat so arranged that when the rotary device is driven by a user to rotate the first guide block, guide rods of the first guide block are moved along a first continuous wave-shaped track of the second guide block, causing the second guide block and the pumping piston to move alternatively up and to further pump air out of the storage container through an air-pimping hole of the piston seat to create a negative pressure. Further, a first spring member an upper rail seat can be provided to balance the movement of the pumping piston and to stabilize the rotation of the first and second guide blocks. A relief valve rod can be selectively used for giving a visual indication indicative of the presence of a negative pressure in the storage container.