This invention relates to a method for boring a large-section tunnel safely and quickly by reinforcing and improving in advance the ground over the full length of the tunnel section, which includes; boring a top drift (2) through the full length of the tunnel (1) section, drilling curved holes inclined in forward or backward directions at an angle of about 45 degrees at preset intervals from the top drift (2) along the peripheral edges of the sections of the tunnel (1) by using ordinary small bore rock drills and curved steel pipes (3), pulling off the steel pipes (3) after inserting injection pipes into the drilled holes, injecting grout into the ground surrounding the tunnel through the injection pipes to develop artificial ground arches (4), excavating the tunnel (1), advancing suspension forms (6) and placing concrete for secondary lining.