The technical scheme of the invention provides a splicing construction method for rebuilt and expanded new and old roads. A step milling position is arranged on a position which is 10cm far away fromthe inner side of an original road traffic lane to avoid a wheel track tape; under a vehicle load function, longitudinal cracks can be effectively reduced; the width of an original road asphalt layermilling step is 45cm; the lime-ash soil aggregates of the original road are milled to form a step of which the width is 25cm; in an early period, the lime earth step of the original road is kept, andis cleared in a later period; the lime earth step and a new water stability base course are jointly paved, so that step integrity and lime earth strength can be guaranteed; and a geogrid of which thewidth is 8m is upwards folded by 25cm along the step, the folded geogrid is fixed by a U-shaped nail on the step, and the skid resistance capability and the bearing capacity of a spliced width roadbedcan be integrally improved. By use of the splicing construction method for rebuilt and expanded new and old roads, complex technologies are reduced, key links are paid attention, construction difficulties are lowered, new and old road splicing quality is improved, and a purpose of efficient construction and stable quality control is realized, and the splicing construction method is good.