Resin bonded sand is a core sand with resin as binder. The regeneration of the old sand is to remove the binder film on the surface of the sand grains to the maximum extent, and to adjust the grain size of the sand grains so that it can be used economically instead of the new sand. The recycled sand can save the consumption of new sand and the transportation cost needed to discard the used sand. Moreover, the recycled sand has uniform surface, smooth surface and good thermal stability, which is beneficial to improving the quality of castings, especially when the resin sand is recycled, the invention can reduce the amount of resin addition, the cost of the resin sand and the environmental pollution caused by the discharged waste sand.