The invention relates to a reusable anti-climbing device at the bottom layer of a tower crane on a building construction site. The reusable anti-climbing device is formed by a steel structure framework; and the steel structure frame is composed of stand columns, truss girders, structural cross beams, a door frame, a door, inclined braces, upright poles, connecting pieces, long auxiliary beams, short auxiliary beams and short beams which are connected and combined through bolts and are respectively standard parts with unified specification. The stand columns are connected to four square ground foundations; and the door with a door lock is arranged in the front of the steel structure framework, a reinforcing mesh is laid at the periphery of the steel structure framework, an anti-falling scaffold board is laid on the roof of the upper layer of the steel structure framework, and a color steel plate is laid on the roof of the lower layer of the steel structure framework. The reusable anti-climbing device at the bottom layer of the tower crane on the building construction site is formed by combining the multiple standard parts which are designed according to conditions such as the sizes of standard knots of the tower crane and design codes for lightweight steel structures. The reusable anti-climbing device has the characteristics of being suitable for the sizes of the standard knots at the bottom layers of different tower cranes, capable of being freely combined, convenient, practical and low in cost, and saving labor and time. The reusable anti-climbing device is convenient to dismantle, is in line with a green construction idea and is safe to use on the site.