Improvement of garage door structure

The utility model relates to a garage door structure, which is provided with a roll motor and a door plate of a three-sheet type. The left and the right of the utility model are respectively provided with a set of gears and chain devices, wherein the roll gear set is formed by combining three gear sheathes of different tooth numbers in one shaft lever. Each gear is matched and sheathed with a chain. One end of the chain is connected to the matched door plate. A guide gear set is arranged at a corresponding position below the roll gear set. The chain is connected with the door plate after passing round the guide gear. Different door plates, such as an upper door plate, a middle door plate and a lower door plate generate different ascending speed and descending speed because of different tooth numbers of the roll gears. Therefore, the effects of accelerating switching speed, average traction force and fixed traction force, succeeded operation and low noise are achieved.