To provide a connecting structure and connecting method of large-sized wall panel, easily and firmly connecting the adjacent large-sized wall panels to each other.

According to this connecting structure and connecting method of large-sized wall panel 1, in connecting the large-sized wall panels 1 formed by joining a plurality of wall panels 2, 2a having frame bodies 4, 5 fitted to the peripheral edge parts of both surfaces of the plate material 3 adjacent to each other in the width direction, an outer facing material 6 is previously fitted to the surface of the frame body 4 of each plate material 3 of the plurality of wall panels 2, 2a, a gypsum board 7 is previously fitted to the surface of the frame body 4 of each plate material 3 with the peripheries of the opposite stile materials 5a, 5b exposed, and after the opposite stile materials 5a, 5b of the adjacent large-sized wall panels 1 are fastened, an auxiliary gypsum board 8 is fitted to the peripheries of the exposed stile materials 5a, 5b. Thus, differently from the past, it is not necessary to perform reinforcement work for maintaining the strength of the panel itself.