The invention provides a slidable tumbling barrel used for a top formwork platform and a construction method thereof. The slidable tumbling barrel comprises two slide rails and a positioning mechanism on the top formwork platform. Each slide rail is provided with an inner side opposite to the other slide rail and an outer side away from the other slide rail. The positioning mechanism is provided with multiple pull hooks which are arranged on the outer sides of the slide rails in a paired mode. A slide seat is arranged on the two slide rails and provided with a hanging opening which is used for clamping and hanging a tumbling barrel body, the tumbling barrel body is hung under the slide seat and is adjusted along with sliding of the slide seat, and the slide seat is hooked by the corresponding paired pull hooks to be positioned. The top formwork platform is provided with the slide rails, the positioning mechanism and the slide seat, after the tumbling barrel body is hung on the slide seat, long-distance sliding distribution can be achieved, and the technical effects of expanding the distribution range, reducing the number of tumbling barrels and construction cost and reducing the dead weight of the top formwork platform are achieved.