The invention belongs to the technical field of building construction. A construction method of a Bailey beam high-altitude long overhanging working platform comprises the following steps that whether the overhanging working platform adopts a pure overhanging construction mode or an outer end pull-up overhanging construction mode is determined, internal force calculation and safety degree accordance are conducted, the construction size of the overhanging working platform is determined, and a construction drawing is drawn; line snapping is conducted on an installation floor according to the construction drawing, and the installation position of a Bailey beam set is determined; with assistance and cooperation of a tower crane, the Bailey beam set is pushed outwards from the floor of a structure body and is anchored and fixed after being pushed in place; and in the overhanging direction, connection shape steel is installed from inside to outside at intervals, supporting plates are laid on the Bailey beam set, a border protection structure is arranged on the periphery of the Bailey beam set, and a dense-mesh safety net is hung. The construction method achieves relatively standardized and programmed construction, effectively guarantees construction safety, greatly improves construction efficiency and construction quality, can be applied and popularized to erection of various working platforms of high-rise building overhanging structures, and has good social benefits and economic benefits.