Primary support structure of underground engineering and construction method thereof

The invention discloses a primary support structure of an underground engineering and a construction method thereof. The method comprises the following steps of along the longitudinal direction of the main body space of the underground engineering to be built, digging a pre-guide hole in the corner of each of the two sides of the upper part of the cross section of the main body space of the underground engineering to be built, wherein the top of each pre-guide hole is higher than the top of the main body space of the underground engineering to be built; in one pre-guide hole, striking a plurality of steel pipes transversely penetrating through the upper soil body of the top of the main body space of the underground engineering to be built into the other pre-guide hole along the transverse direction of the main body space of the underground engineering to be built to form a transverse pipe shed; after supporting and fixing the two ends of the steel pipes in the transverse pipe shed, forming the primary support structure of the underground engineering. By the construction method, the construction progress of the primary support structure of the underground engineering can be quickened, and then the construction period of the underground engineering is shortened.