The invention provides a frozen-dough bread premixing powder and a preparation method thereof. The frozen-dough bread premixing powder includes a frozen dough improver, a high-gluten wheat flour, oat flour, edible salt, white granulated sugar, milk powder and yeast. The frozen dough improver refers to one or a mixture of glucose oxidase, xylanase, alpha-amylase, fatty acid monoglyceride, fatty acid diglyceride, calcium sulfate, calcium dihydrogen phosphate, tricalcium phosphate, ascorbic acid, trehalose, wheat gluten powder, sodium polyacrylate and corn starch. By means of an emulsifier, oil and water are fully combined and mixed in dough, the dough, oil and water can be fully kneaded together, a more excellent water water-retaining property is obtained, and products thus have more advantages in softness, preservation duration and shelf life. The frozen-dough bread premixing powder using the frozen dough improver can avoid the deterioration of the dough at low temperature, the shelf life is prolonged, and the quality of the frozen dough is improved.