Abstract: A sealing cover includes a base, a lower lid, and a soft, deformable gasket mounted between outer peripheries of the base and the lower lid. An upper lid includes a positioning hole having an inner periphery with higher and lower positioning grooves, with a lower positioning groove located between two adjacent higher positioning grooves. A positioning ring includes upper and lower positioning protrusions. The upper lid can be pressed and moved downward relative to the lower lid, so that the pressing member presses against the upper positioning protrusions of the positioning ring, causing rotational movement of the positioning ring through an angle and changing the spacing between the base and the lid. When the upper lid is released, the upper positioning protrusions are engaged in higher positioning grooves or the lower positioning grooves so that the sealing cover is in a sealing state or an unsealing state.