The invention discloses a structure-adjustable three-freedom-degree parallel mechanism which comprises a fixed platform, a movable platform and three branches. Each branch comprises an adjusting part, a column, a moving pair, a rotating pair, a connecting rod and a spherical pair, wherein the adjusting part consists of a sliding rail, a slide block, an inlaid strip and a screw. The sliding rail of the adjusting part is horizontally installed on the fixed platform and is matched with a sliding groove formed in the lower portion of the slide block, the column is vertically installed on the slide block, the moving pair is connected with the column, the axis of the moving pair is perpendicular to the sliding groove formed in the lower portion of the slide block and is connected with the rotating pair, the axis of the rotating pair is parallel to the upper plane of the fixed platform, one end of the connecting rod is connected with the rotating pair, the other end of the connecting rod is connected with the spherical pair, and the spherical pair is installed on the movable platform. The angles of the three columns are adjusted through the sliding rails and the sliding grooves, the arrangement form of the connecting rods can be conveniently and quickly adjusted, installation is facilitated through quick fixing of the inlaid strips and the screws, the adjusting time is saved, and the efficiency is improved.