Abstract: The present invention is to provide an umbrella structure including at least one mushroom-shaped hub, a plurality of supporting members, and a main rod. Each mushroom-shaped hub has a hollow tubular body, two openings at two opposite ends respectively, and a cap portion located near a first opening and formed with a plurality of evenly distributed grooves which extend in the radial direction of the first opening. The supporting member has one end whose diameter is less than the diameter of the first opening but greater than the width of each groove and which therefore can pass through the first opening and be received in the cap portion. Thus, when the main rod penetrates the two openings, the end of each supporting member can be limited in position in the cap portion, and the remaining portion thereof can extend out of the cap portion and move along the groove accordingly.