The invention provides a preparation method for regenerative polyester staple fiber, comprising the following steps: drying polyester regenerated material, mixing the polyester regenerated material with inorganic granule, melting by a screw melt extrusion spinning machine, spinning, cooling, bundling and applying oil, falling bucket in reciprocating manner and bundling; carrying out first-stage oil bath traction by a traction machine, carrying out second-stage steam traction by the traction machine, carrying out tension heat shaping by the traction machine, cooling and applying oil, carrying out three-stage tension by the traction machine, and cutting by a staple fiber cutting machine; the method has low production cost, high efficiency, energy-saving and environment-friendly performances; the fiber prepared by the invention has high density, large oil absorbing quantity and has good dispersity, and is not easy to intertwist, thereby improving mechanical property, remarkably reducing thermal shrinkage and aging resistance; and, the bond stress with the aggregate is enhanced in the asphalt concrete, thereby remarkably improving the reinforcing effect of asphalt concrete.