Based on the overpass project over Beijing-Hong Kong-Macao Expressway on Changsha Pan-Pan Road，this paper proposed a construction method of large-slope walking-type incremental launching and high falling beam of steel box girder given the difficulties in busy traffic under the bridge，large pushing slope，and great total height of falling beam.After the steel box girder assembly was completed，some bridge deck ancillary facilities were constructed in advance in the preassembly yard and the weight was allocated.The steel box girder was pushed synchronously，thereby reducing the aerial work on the bridge in the later stage.During the incremental launching construction of the steel box girder above the large-slope approach bridge，the alignment of the steel box girder was adjusted by cyclic grading of the rear fulcrum.When high falling beam was carried out on the temporary pier，the drop beam hanging system was set on the bottom plate of the steel box girder，and the child and mother double circulation mode was adopted.The high falling beam was converted into continuous graded low falling beam by repeatedly “top-down ” method between the crawler shelf pier，the crawler slider，and the replacement pier.By analyzing the elevation matching and constraint conditions of incremental launching and falling beam systems in each process conversion，this paper established the system elevation calculation formula suitable for the general situation and gave a reasonable parameter range.