The utility model discloses an overlarge cross section old loess tunnel primary support structure of a high-speed railway, which aims to meet the requirements on the stability and the supporting safety of a tunnel to ensure that construction operations are move convenient and the construction cost is reduced. The overlarge cross section old loess tunnel primary support structure comprises a sprayed concrete layer (10) of a closed surrounding rock and full-ring steel frames embedded in the tunnel primary support structure, wherein the full-ring steel frames are arranged at intervals along the excavation direction of the tunnel; two adjacent full-ring steel frames are fixedly connected together by a connecting component; the full-ring steel frames are full-ring grille steel frames (20); and the 24h early strength of the sprayed concrete layer (10) reaches 12 MPa. The overlarge cross section old loess tunnel primary support structure has the advantages that: the griller steel frames can meet the requirements on the stability and the supporting safety of the tunnel, can greatly reduce the steel consumption and reduce the construction cost; an advancing small guiding pipe can pass through internal gaps of the grille steel frames freely, and the construction operations are more convenient; and the contact surfaces of the grille steel frames and primary sprayed concrete are two reinforcing steel bars, the contact surfaces are small, and the sprayed concrete is very easy to become compact.