Outboard template construction method of post-pouring belt of outer wall of underground structure

The invention relates to a building construction method, in particular to an outboard template construction method of a post-pouring belt of an outer wall of an underground structure, which comprises the following steps of: freely taking steel bar wastes produced in a construction site, binding a precast slab reinforcement cage in a single-row two-way binding way, wherein the width is more than that of the post-pouring belt and the length is 1 or 1.2 m; after the reinforcement cage is bound, binding a fixed precast slab steel wire at the intersection of transverse and longitudinal steel bars, wherein the extension length of the steel wire is 400-500 m and the binding position of the steel wire is arranged in a quincunx way; using a 5*10 mm or 10*10 mm wood beam as a precast slab template; after the reinforcement cage is bound and formed and the template is supported, pouring precast slabs when residue concrete is provided on site, wherein the thickness is 50 mm; and when an excessive trough is backfilled, bin