The invention relates to a small-angle bottom-penetrating construction method of a highway grid tunnel. The cross section of a tunnel is separated into a left upper area, a left lower area, a middle upper area, a middle lower area, a right upper area, and a right lower area in the vertical and horizontal directions. The construction method comprises the following steps of when the areas are excavated, excavating the middle area of the tunnel, and arranging an advance pre-support around the contour of the cross section of the tunnel before the middle area is excavated; after the middle area of the tunnel is excavated for a section of distance, excavating the areas at both sides of the tunnel from top to bottom, wherein when the area is excavated, the staggering distance is 3-5m at a working surface in the excavation process of a tunnel chamber, and the circulation excavation progress is 0.5m each time. The construction method has the advantages that the small-angle bottom-penetrating construction of the highway tunnel is realized, the normal passing of highways is guaranteed, the settlement of road pavements meets the design requirements, the site construction safety, quality and construction period goals are controllable, and the construction method can be applied to busy roads, such as airport highways.