The invention relates to an overpass top-down construction method suitable for a loess area. The overpass top-down construction method effectively solves the problems that the time for erecting a temporary bridge and constructing a support in the overpass construction is long, the cost is high, and the safety risks are high. According to the technical scheme, the method aims to adjust an overall construction procedure and optimize a construction process, and comprises the steps of firstly widening an original road at the position of an overpass; forming holes in the overpass pile foundations in a manual hole digging manner; during the hole forming process, increasing the pier stud top elevation to the pile top elevation diameter; reserving the pier column construction space, simulating underwater concrete pouring pile forming through a guide pipe for the pile foundation, carrying out steel formwork sectional construction on the pier columns, reserving the tie beam steel bar joints during pier column steel bar machining, after pier column construction is completed, carrying out the box girder, anti-collision wall, bridge deck pavement and other upper structure construction, and thencarrying out earth excavation after the overpass is opened to traffic. The construction method can effectively shorten the construction period and reduce the construction cost and the construction safety risk.