The invention discloses a steel structure building body, a corner wall body structure and a construction method. Two sides of the corner wall body are provided with a first horizontal structure board and a second horizontal structure board; a first vertical structure board is arranged outside a vertical wall body and on one end of the horizontal wall body; the inner side of the vertical wall body is provided with a second vertical structure board; a first angle iron is arrange between the first horizontal structure board and the horizontal wall body and is fixed through a bolt; and a second angle iron is arranged between the second horizontal structure board and the horizontal wall body and is fixed through a bolt. The corner wall body structure solves a problem of outer wall connection at a corner, realizes reliability and convenience of the connection at the wall corner, guarantees stable connection of the wall body, improves construction efficiency, and saves materials. Besides, the insulation material is integrated and has good insulation performance.