A combination structure of a door that is equipped on a vehicle may include an upper rail formed by bending a metal plate and disposed to correspond to an edge of a door glass, an inner panel disposed by a distance from the upper rail to form an insertion hole and one side of the inner panel is fixed to the upper rail, a frame molding in which a protrusion portion is formed on at least one side thereof and the protrusion portion is inserted into the insertion hole formed between the upper rail and the inner panel, a vehicle body disposed by a distance from the inner panel, and a first sealing member and a second sealing member.