The invention discloses a method for preparing a Cu-doped SiO2 nano composite aerogel. The method comprises the following steps: dissolving Cu(NO3)2.3H2O into absolute ethyl alcohol, adding tetraethylorthosilicate and deionized water, stirring, adding DMF and concentrated nitric acid, continuing to stir for 6.5-7.5 h, pouring a sol into a culture dish, aging for 3-5 d, and thus obtaining a precursor composite alcogel; then continuing to age the obtained alcogel for 23-25 h at the temperature of 25-35 DEG C, soaking in a mixed solution of tetraethyl orthosilicate and absolute ethyl alcohol atthe constant temperature of 34-36 DEG C, soaking for 2-3 d, washing, carrying out constant temperature drying at the temperature of 34-36 DEG C for 14-16 h, and carrying out constant temperature drying at the temperature of 60-65 DEG C for 71-73 h; and finally, putting the sample into an electric furnace, treating for 4-6 h at the temperature of 740-760 DEG C, and then cooling. The composite aerogel prepared by the method has the advantages of small particle size, large specific surface area, perfect microstructure and good thermal stability.