A valve apparatus of the present invention includes a body, a seat and a cap, in which the body includes a chamber and passageway therein, the chamber is connected with the passageway, and the body includes a first ladder toward the passageway. The seat is disposed in the passageway. The seat includes a second ladder toward the first ladder of the body, and the second ladder of the seat is engaged with the first ladder of the body. The seat also includes a third ladder opposite to the second ladder. The cap has a flange which is contacted with the third ladder of the seat to fix the seat in the body tightly so that the cap is against the seat to prevent the seat from pulling out of the valve apparatus.