A vertical joint coupling structure includes a first casing in which combustion gases flow, a second casing connected to the first casing, a vertical joint mounted on the second casing and coupled to the first casing, a plurality of bolt fasteners fastened to the vertical joint and the first casing, a plurality of jacking screws inserted into the vertical joint to secure a gap between the vertical joint and the first casing upon disassembly or assembly between the first casing and the second casing, and a shim member inserted into the gap between the vertical joint and the first casing.