The utility model discloses an upper side beam of a wagon shed 70, belongs to the field of cold-formed steel products, and particularly relates to an upper side beam applied to a wagon steel structure. The upper side beam comprises an outer beam and an inner beam, an upper side beam body is an L-shaped hollow beam, the L-shaped outer beam is positioned on the outer side of the upper side beam body, an L-shaped body of the outer beam is longer than that of the inner beam, the L-shaped inner beam is positioned on the inner side of the upper side beam body, the L-shaped body of the inner beam is shorter than that of the outer beam, an opening connected by the outer beam and the inner beam points on the lower inner side of the upper side beam body, a notch of the opening is connected with a fixed side curtain sliding rail and two movable vertical column sliding rails, the mounting height of each movable vertical column sliding rail is higher than that of the side curtain sliding rail, a cord fabric is arranged on the side curtain sliding rail, and a movable plate is connected onto movable vertical columns of the two adjacent movable vertical column sliding rails in an inserted manner. Welding lines are smooth and even, and the technical route of changing round into square is adopted. The requirement on embedded assembly is met, and the upper side beam has the advantages of fewer working hours and short construction period.