A panel structure of a steel house and a panel construction method. In the panel structure, surface materials are tightly stretched on a frame formed by assembling sheet lightweight channel steels in a rectangular shape to form a wall panel, the wall panels are disposed along the four sides of a rectangular shape to form walls on floors, and the wall panels are assembled with floor panels formed by placing floor plates on floor joists to construct a structural skeleton of multiple stories. The panel structure is characterized in that the side end parts of the floor panels are connected to the inner wall side upper ends of the lower story wall panels, and the end edges of the upper and lower story wall panels on at least two opposed sides among the wall panels disposed on the four sides are abutted on and joined to each other.