A method of making a buffer board of a treadmill includes a sizing step, a shade drying step, a presetting step, a clamping and heat-pressing step, a cooling step, and a die opening step. The method can easily make the desired buffer board adapted to the treadmill and can only change different dies to make buffer boards with different structures when an upper die and a lower die of a die set provide protrusions, flat surfaces or depressed surfaces, thereby reducing the manufacturing cost.