The invention discloses a low-density refractory fiber coating and a preparation method thereof, and relates to a refractory fiber coating. The low-density refractory fiber coating consists of the following components in percentage by weight: 23-50% of refractory fiber cotton, 10-20% of hollow ball, 27-36% of bonding clay, 0-6% of high alumina bauxite fine powder, 8-12% of high alumina cement and 3-5% of a bonding agent. The low-density refractory fiber coating is obtained through the steps of burdening, mixing, stirring and coating; on the basis that the heat insulation performance is good, the volume density of the coating is reduced, the volume stability of material is improved, and the purpose of improving the bonding effect on relatively thick heat-insulation layer coating is realized.