The invention provides a simple wellhead device and an application method thereof, and belongs to the field of petroleum exploration. The simple wellhead device comprises a cover plate flange (1), an assistant flat valve (2), a main flat valve (3), a small tee joint (4) and an instrument flange (5) which are sequentially connected; an upper end port of the small tee joint (4) is connected with the instrument flange (5), and while a lower end port of the small tee joint (4) is connected with an upper connector of the main flat valve (3); a side flange is mounted at the side end port of the small tee joint (4), wherein the side flange is a threading flange with a screwed plug, and a screwed flange is arranged on the side flange and can be blocked with a plug in general condition. With the adoption of the method, the change on pressure of a wellhead of a completed well can be monitored on real time.