A waterproof lockable door and a pressure adjusted plug thereof are provided. An electronic device is formed with an opening having an annular wall. The waterproof lockable door includes a cover member having at least one through hole and a pressure adjusted plug including a waterproof member and at least one fastening unit. The waterproof member includes at least one fastening hole. The fastening unit is formed with a head portion and a rod portion, and the rod portion is received in the through hole and moves relative to the cover member, thereby driving the outer periphery of the waterproof member to be tightly adjacent to annular wall. Accordingly, the tolerance of the annular wall and the waterproof member and the air pressure inside an opening both force the waterproof member to move.