The invention discloses a piece of highly-resistant-to-water core-level glass fiber air filtering paper. The filtering paper comprises glass fiber filtering paper made from alkali-free glass fiber with the diameter being 0.1-0.3mu m, 0.5-0.7mu m and 0.8-1.0mu m and from alkali-free glass long fiber with the diameter being 1.4-1.6mu m, and a water-resistant layer attached to the face of the filtering paper and formed by hydrogen silicon oil and acrylic emulsion. The invention also discloses a preparing method for the air filtering paper, which comprises the steps of 1, selecting raw materials according to a proportion, 2, performing pulping to disperse the raw materials to obtain pulp, 3, diluting the pulp and adjusting the PH value, 4, performing slag-removing on the pulp in the step 3 and obtaining wet paper by wet forming, 5 dehydrating the wet paper in the step 4, 6, spraying mixing emulsion of the hydrogen silicon oil, the acrylic emulsion and water on the surface of the wet paper in the step 5; and 7, drying the wet paper in the step 6. The glass fiber air filtering paper has excellent water-resistant property and is suitable for severe environment.