The invention relates to a preparation method of a mullite-fibrofelt-reinforced SiO2-Al2O3 aerogel composite heat-insulating material, which comprises the following steps: by using surface-pretreated mullite fibrofelt as a reinforcer, tetraethyl orthosilicate as a silicon source, cheap inorganic aluminum salt as an aluminum source and epoxide as a network formation agent, uniformly mixing, and carrying out sol-gel, aging and supercritical drying to obtain the mullite-fibrofelt-reinforced SiO2-Al2O3 aerogel composite heat-insulating material. In the preparation process, no catalyst is needed, and a one-step method is adopted to greatly optimize the preparation technique. Thus, the heat-insulating material has the advantages of low cost, smooth surface and controllable thickness, and can resist the temperature of 1200 DEG C in an air atmosphere. The room temperature thermal conductivity is 0.023-0.027 W.m<-1>K<-1>, and the apparent density is 0.18-0.22 g/cm<3>. The method has the advantages of simple materials, low cost and simple technique, is simple to operate in the technical process, and can easily implement large-scale production.