A tie-down kit for supporting a boat cover is primarily composed of a disk, a length adjustable pole and a rope. The disk bottom is provided with a flange having a hole, and two cross grooves on the top. The top end of the length adjustable pole is inserted into the hole of the flange, while the bottom end of the length adjustable pole has a base. One end of the rope goes through the two grooves at the top of the disk. Thereby, with the length adjustable pole disposed in the boat for adjusting an appropriate height, and the rope bound around the bow and stern of the boat, when the boat cover is mounted on the hull, it can be perfectly supported.