Leakproof cup lid having inner-outer double-engagement structure

A leakproof cup lid having an inner-outer double-engagement structure, comprising a lid top and a sealing flange, the sealing flange being an annular body formed by bending an edge of the lid top, wherein the sealing flange includes an inner snap and an outer snap, the inner snap is located on an inner side and recessed downward, the outer snap is located on an outer side and protrudes upward, an insertion slot is formed facing downward between the inner snap and the outer snap, when the cup lid is placed on the cup body, a top end of the cup body is able to be inserted into the insertion slot, and the outer snap and the inner snap cooperate to seal and clamp an inner top wall and an outer top wall of the cup body;

• wherein the lid top includes a lid body and a cover plate, a center part of the lid body is recessed to form a temporary storage chamber, a lower vent hole communicating with the temporary storage chamber is formed in the center part of the lid body, the cover plate is capable of opening and sealing the temporary storage chamber, an upper vent hole is formed on the cover plate, and the upper vent hole and the lower vent hole are offset from each other, a buffering backflow structure is provided in the temporary storage chamber for buffering flow of liquid from the lower vent hole toward the upper vent hole and guiding the liquid back into the cup body through the lower vent hole, the buffering backflow structure includes a first liquid-blocking step, which is formed by an upward protrusion from a bottom part of the temporary storage chamber on a side close to the upper vent hole, a step surface of the first liquid-blocking step inclines downward from the center part toward a peripheral part.