The invention discloses a post-cast strip construction method of a large area roofing building with a main beam passing through a post-cast strip. The construction method includes the following stepsthat lifting rings are pre-buried in the positions, located on the post-cast strip (5), of the main beam (3); concrete is poured, and the pre-buried lifting rings are exposed in the position, locatedon the post-cast strip, of the main beam (3); two temporary supports (1) are arranged on the two sides of the post-cast strip (5); a temporary structural steel beam (2) is erected on each of the two temporary supports (1); and after the strength of the portions, located on the two sides of the post-cast strip (5), of the main beam (3) meets design requirements, wire ropes (4) are installed betweenthe temporary structural steel beams (2) and the pre-buried lifting rings to fix. According to the post-cast strip construction method, in the period of waiting for pouring of the post-cast strip (not less than 28 days in general according to the specifications), a construction space below the main beam (3) can be impervious to an original erected scaffold, multiple working procedures can be conducted simultaneously, the building efficiency is improved, and the construction cost is reduced.