Tightness self-checking device for waterproof mobile phone protective case and method thereof

A tightness self-checking device for a waterproof mobile phone protective case, comprising:

• a waterproof mobile phone case cavity, wherein a front-mounted mobile phone case is provided on a front side of the waterproof mobile phone case cavity, a lower part of the front-mounted mobile phone case is provided with an opening;
• a tightness self-checking mechanism, is mounted inside the opening;
• and
• an engagement mechanism, is mounted at a front edge of the waterproof mobile phone case cavity;
• wherein the tightness self-checking mechanism comprises a pressing frame, a fixing frame and a front transparent soft film, the pressing frame is placed inside the opening, retaining grooves are equidistantly provided in a front periphery of the pressing frame, the retaining grooves are all engaged with buckles, the buckles are all buckled at an inner edge of the fixing frame, a foldable soft rubber cavity is fixedly connected to a front side of the fixing frame, a pressing plate is fixedly connected to a front side of the foldable soft rubber cavity, and the front transparent soft film is mounted on an inner rear side of the front-mounted mobile phone case.