The invention discloses a connecting structure of a steel-structure roof. The structure comprises roof beams, supporting bars disposed on the roof beams and purlines which are fixed on the supporting bars by bolts, wherein color steel plates and day lighting plates are disposed on the purlines, and the color steel plates and the day lighting plates are connected in a staggered manner; the included angle between the steel-structure roof and the horizontal plane is 5 DEG, each day lighting plate is disposed between every two color steel plates, one end of the day lighting plate is disposed under the upper color steel plate, the other end is disposed on the lower color steel plate, the color steel plates and the day lighting plates are fixed on the purlines by fixation bolts, and a sealing adhesive is disposed at joints between the color steel plates and the day lighting plates; and the adjacent color steel plates are occluded at the joints. The structure disclosed by the invention has the advantages that sealing performance of the steel-structure roof can be enhanced obviously; and the structure is highly resistant to wind and rain and can effectively prolong the service life.