A preparation method of a buffer comprises the following preparation steps: at first, mixing No. 2 Bangni thermosetting resin with quartz sand to obtain sand for preparing a sand shell of the buffer, wherein the using amount of the thermosetting resin is 1.3%-2.0% of the weight of the quartz sand; then placing the sand in a sand shooting machine to obtain the sand shell with a buffer cavity; next pouring molten metal obtained through smelting raw materials of the buffer in the sand shell; and within 0.6-1.5 h after the pouring is finished, conducting pyrolysis devolatilization on the No. 2 Bangni thermosetting resin in the sand shell, and scattering the quartz sand from the condensed metal surface to obtain the buffer. The preparation method has the advantages that the sand is scattered completely, manual sanding is not required, and the production cost is low.