The invention belongs to the technical field of electrothermal materials, and particularly relates to a Cu-Te (copper-thulium) nanocrystalline/Cu2SnSe3 (copper and tin selenide) electrothermal composite material and a preparation method thereof. The volume ratio of the Cu-Te nanocrystalline in the composite material is 0.2 to 1.2%. The prepared Cu-Te (copper-thulium) nanocrystalline/Cu2SnSe3 electrothermal composite material has the advantages that the better electrothermal property is realized, and the ZT value of the Cu2SnSe3 matrix is greatly improved; the operation of the required preparation technology is simple, the parameters are controllable, and the composite material is suitable for larger-scale production.