The invention relates to the technical field of food processing, in particular to low-GI high-proportion purple sweet potato whole flour noodles and a preparation method thereof. The low-GI high-proportion purple sweet potato whole flour noodles are prepared from, by weight, 90-110 parts of wheat flour, 40-100 parts of sweet potato whole flour, 10-40 parts of wheat bran, 0.02-0.06 part of isoamylase, 0.6-2.0 parts of konjac manna and 0.8-4.2 parts of vital gluten. The low-GI high-proportion purple sweet potato whole flour noodles and the preparation method thereof effectively solve the technical problems that the high-proportion purple sweet potato noodles have unsmooth flour bands, stick to a roller, have poor tensile resistance, are easy to break, have large cooking loss and the like bytaking the wheat flour, the sweet potato whole flour, the wheat bran, the isoamylase, the konjac manna and the vital gluten as raw materials through a three-layer compound calendaring technology, andhave the advantages that a bio-enzyme technology is utilized, and the isoamylase is added for modifying starch, which increases the content of resistant starch in flour, effectively reduces GI of thenoodles, not only can ensure the requirements of special crowd with type 2 diabetes for the noodles, but also can ensure the quality of the noodles.