The invention discloses an open-graded lignin fiber asphalt mixture and a preparation method thereof. The mixture comprises SBS modified asphalt, lignin fiber and mineral aggregate, wherein the mineral aggregate is composed of aggregate and mineral powder; and the aggregate is divided into three groups according to the particle sizes of 10-15mm, 5-10mm and less than or equal to 3mm. The preparation method of the mixture comprises the following steps: respectively drying the raw materials to constant weight; performing dry mixing on the lignin fiber and the coarse and fine aggregate for 30 seconds at a mixing temperature, adding the constant temperature SBS modified asphalt for performing wet mixing for 3 minutes, and adding the mineral powder for mixing for 90 seconds, thereby obtaining the product. According to the open-graded lignin fiber asphalt mixture provided by the invention, the pavement performance of the mixture can be greatly improved, the operation is simple and convenient,and the cost is saved.